Reducing layer-2 protocol overhead by improving layer processing efficiency

ABSTRACT

The layer processing includes at least processing on a first, a second and a third layer. At the transmitter side, the third layer receives a packet, adds its header and forwards the packet to the second layer. The second layer performs segmentation and provides segmented data to the first layer, which maps the segmented data onto physical resources. The segmentation is based on the allocated resources. Retransmissions may take place on the third layer and thus, the third layer may re-segment the packet according to the received feedback for particular segments and provide the re-segmented data to the lower layers. Alternatively, the feedback information is provided to the second layer which then performs the segmentation by taking it into account. Correspondingly, the receiver performs re-ordering and re-assembly at the third layer for which it receives also control information from the second layer.

BACKGROUND 1. Technical Field

The present disclosure relates to transmission and reception processingon multiple layers in a communication system as well as to thecorresponding transmission apparatuses, methods and programs.

2. Description of the Related Art

Third-generation mobile systems (3G) based on WCDMA radio-accesstechnology are being deployed on a broad scale all around the world. Afirst step in enhancing or evolving this technology entails introducingHigh-Speed Downlink Packet Access (HSDPA) and an enhanced uplink, alsoreferred to as High Speed Uplink Packet Access (HSUPA), giving aradio-access technology that is highly competitive. In order to beprepared for further increasing user demands and to be competitiveagainst new radio access technologies, 3GPP introduced a new mobilecommunication system called Long Term Evolution (LTE). LTE is designedto meet the carrier needs for high speed data and media transport aswell as high capacity voice support through to the next decade. Theability to provide high bit rates is a key measure for LTE. The workitem (WI) specification on Long-Term Evolution (LTE) called Evolved UMTSTerrestrial Radio Access (UTRA) and UMTS Terrestrial Radio AccessNetwork (UTRAN) is finalized as Release 8 (Rel. 8 LTE). The LTE systemrepresents efficient packet based radio access and radio access networksthat provide full IP-based functionalities with low latency and lowcost. In LTE, scalable multiple transmission bandwidths are specifiedsuch as 1.4, 3.0, 5.0, 10.0, 15.0, and 20.0 MHz, in order to achieveflexible system deployment using a given spectrum. In the downlink,Orthogonal Frequency Division Multiplexing (OFDM) based radio access wasadopted because of its inherent immunity to multipath interference (MPI)due to a low symbol rate, the use of a cyclic prefix (CP), and itsaffinity to different transmission bandwidth arrangements.Single-carrier frequency division multiple access (SC-FDMA) based radioaccess was adopted in the uplink, since the provision of wide areacoverage was prioritized over improvement in the peak data rateconsidering the restricted transmission power of the user equipment(UE). Many key packet radio access techniques are employed includingmultiple-input multiple-output (MIMO) channel transmission techniques,and a highly efficient control signaling structure is achieved in Rel. 8LTE.

LTE Architecture

The overall architecture is shown in FIG. 1 and a more detailedrepresentation of the E-UTRAN architecture is given in FIG. 2. TheE-UTRAN consists of eNBs, providing the E-UTRA user plane(PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towardsthe UE. The eNB hosts the Physical (PHY), Medium Access Control (MAC),Radio Link Control (RLC), and Packet data Control Protocol (PDCP) layersthat include the functionality of user-plane header-compression andencryption. It also offers Radio Resource Control (RRC) functionalitycorresponding to the control plane. It performs many functions includingradio resource management, admission control, scheduling, enforcement ofnegotiated UL QoS, cell information broadcast, ciphering/deciphering ofuser and control plane data, and compression/decompression of DL/UL userplane packet headers. The eNBs are interconnected with each other bymeans of the X2 interface. The eNBs are also connected by means of theS1 interface to the EPC (Evolved Packet Core), more specifically to theMME (Mobility Management Entity) by means of the S1-MME and to theServing Gateway (S-GW) by means of the S1-U. The S1 interface supports amany-to-many relation between MMEs/Serving Gateways and eNBs. The SGWroutes and forwards user data packets, while also acting as the mobilityanchor for the user plane during inter-eNB handovers and as the anchorfor mobility between LTE and other 3GPP technologies (terminating S4interface and relaying the traffic between 2G/3G systems and PDN GW).For idle state UEs, the SGW terminates the DL data path and triggerspaging when DL data arrives for the UE. It manages and stores UEcontexts, e.g. parameters of the IP bearer service, network internalrouting information. It also performs replication of the user traffic incase of lawful interception.

The MME is the key control-node for the LTE access-network. It isresponsible for idle mode UE tracking and paging procedures includingretransmissions. It is involved in the bearer activation/deactivationprocess and is also responsible for choosing the SGW for a UE at theinitial attach and at time of intra-LTE handover involving Core Network(CN) node relocation. It is also responsible for authenticating the user(by interacting with the HSS). The Non-Access Stratum (NAS) signalingterminates at the MME and it is also responsible for generation andallocation of temporary identities to UEs. It checks the authorizationof the UE to camp on the service provider's Public Land Mobile Network(PLMN) and enforces UE roaming restrictions. The MME is the terminationpoint in the network for ciphering/integrity protection for NASsignaling and handles the security key management. Lawful interceptionof signaling is also supported by the MME. The MME also provides thecontrol plane function for mobility between LTE and 2G/3G accessnetworks with the S3 interface terminating at the MME from the SGSN. TheMME also terminates the S6a interface towards the home HSS for roamingUEs.

The downlink component carrier of a 3GPP LTE system is subdivided in thetime-frequency domain in so-called subframes. In 3GPP LTE each subframeis divided into two downlink slots, wherein the first downlink slotcomprises the control channel region (PDCCH region) within the firstOFDM symbols. Each subframe consists of a give number of OFDM symbols inthe time domain (12 or 14 OFDM symbols in 3GPP LTE (Release 8)), whereineach OFDM symbol spans over the entire bandwidth of the componentcarrier. The OFDM symbols thus each consists of a number of modulationsymbols transmitted on respective subcarriers.

Assuming a multi-carrier communication system, e.g. employing OFDM, asfor example used in 3GPP Long Term Evolution (LTE), the smallest unit ofresources that can be assigned by the scheduler is one “resource block”.A physical resource block (PRB) is defined as consecutive OFDM symbolsin the time domain (e.g. 7 OFDM symbols) and consecutive subcarriers inthe frequency domain (e.g. 12 subcarriers for a component carrier). In3GPP LTE (Release 8), a physical resource block thus consists ofresource elements, corresponding to one slot in the time domain and 180kHz in the frequency domain (for further details on the downlinkresource grid, see for example 3GPP TS 36.211, “Evolved UniversalTerrestrial Radio Access (E-UTRA); Physical Channels and Modulation(Release 8)”, section 6.2, available at http://www.3gpp.org).

One subframe consists of two slots, so that there are 14 OFDM symbols ina subframe when a so-called “normal” CP (cyclic prefix) is used, and 12OFDM symbols in a subframe when a so-called “extended” CP is used. Forsake of terminology, in the following the time-frequency resourcesequivalent to the same consecutive subcarriers spanning a full subframeis called a “resource block pair”, or equivalent “RB pair” or “PRBpair”.

The term “component carrier” refers to a combination of several resourceblocks in the frequency domain. In future releases of LTE, the term“component carrier” is no longer used; instead, the terminology ischanged to “cell”, which refers to a combination of downlink andoptionally uplink resources. The linking between the carrier frequencyof the downlink resources and the carrier frequency of the uplinkresources is indicated in the system information transmitted on thedownlink resources. Similar assumptions for the component carrierstructure apply to later releases too.

General Overview of the OSI Layer

FIG. 3A provides a brief overview of a layer model on which the furtherdiscussion of the LTE architecture is based.

The Open Systems Interconnection Reference Model (OSI Model or OSIReference Model) is a layered abstract description for communication andcomputer network protocol design. The OSI model divides the functions ofa system into a series of layers. Each layer has the property of onlyusing the functions of the layer below, and only exporting functionalityto the layer above. A system that implements protocol behaviorconsisting of a series of these layers is known as a ‘protocol stack’ or‘stack’. Its main feature is in the junction between layers whichdictates the specifications on how one layer interacts with another.This means that a layer written by one manufacturer can operate with alayer from another. For the purposes of the present disclosure, only thefirst three layers will be described in more detail below.

The physical layer or layer 1's main purpose is the transfer ofinformation (bits) over a specific physical medium (e.g. coaxial cables,twisted pairs, optical fibers, air interface, etc.). It converts ormodulates data into signals (or symbols) that are transmitted over acommunication channel.

The purpose of the data link layer (or Layer 2) is to shape theinformation flow in a way compatible with the specific physical layer bybreaking up the input data into data frames (Segmentation AndRe-assembly (SAR) functions). Furthermore, it may detect and correctpotential transmission errors by requesting a retransmission of a lostframe. It typically provides an addressing mechanism and may offer flowcontrol algorithms in order to align the data rate with the receivercapacity. If a shared medium is concurrently used by multipletransmitters and receivers, the data link layer typically offersmechanisms to regulate and control access to the physical medium.

As there are numerous functions offered by the data link layer, the datalink layer is often subdivided into sublayers (e.g. RLC and MAC layersin UMTS). Typical examples of Layer 2 protocols are PPP/HDLC, ATM, framerelay for fixed line networks and RLC, LLC or MAC for wireless systems.More detailed information on the sublayers PDCP, RLC and MAC of layer 2is given later. It is noted that in the present application thesublayers are also referred to as “layer” and thus the term “layer”employed herein does not necessarily mean a layer of the OSI model.

The network layer or Layer 3 provides the functional and proceduralmeans for transferring variable length packets from a source to adestination via one or more networks while maintaining the quality ofservice requested by the transport layer. Typically, the network layer'smain purposes are inter alia to perform network routing, networkfragmentation and congestion control functions. The main examples ofnetwork layer protocols are the IP Internet Protocol or X.25.

With respect to Layers 4 to 7, it should be noted that depending on theapplication and service it is sometimes difficult to attribute anapplication or service to a specific layer of the OSI model sinceapplications and services operating above Layer 3 often implement avariety of functions that are to be attributed to different layers ofthe OSI model. Therefore, especially in TCP(UDP)/IP based networks,Layer 4 and above is sometimes combined and forms a so-called“application layer”.

Layer Services and Data Exchange

In the following, the terms service data unit (SDU) and protocol dataunit (PDU) as used herein are defined in connection with FIG. 3B. Inorder to formally describe in a generic way the exchange of packetsbetween layers in the OSI model, SDU and PDU entities have beenintroduced. An SDU is a unit of information (data/information block)transmitted from a protocol at layer N+1 that requests a service from aprotocol located at layer N via a so-called service access point (SAP).A PDU is a unit of information exchanged between peer processes at thetransmitter and at the receiver of the same protocol located at the samelayer N.

A PDU is generally formed by a payload part consisting of the processedversion of the received SDU(s) preceded by a layer N specific header andoptionally terminated by a trailer. Since there is no direct physicalconnection (except for Layer 1) between these peer processes, a PDU isforwarded to the layer N−1 for processing. Therefore, a layer N PDU is,from a layer N−1 point of view, an SDU.

LTE User Plane (U-Plane, UP) and Control Plane (C-Plane, CP) Protocols:

The LTE layer 2 user-plane/control-plane protocol stack comprises threesublayers PDCP, RLC and MAC.

As explained before, at the transmitting side, each layer receives a SDUfrom a higher layer for which the layer provides a service and outputs aPDU to the layer below. The RLC layer receives packets from the PDCPlayer. These packets are called PDCP PDUs from a PDCP point of view andrepresent RLC SDUs from an RLC point of view. The RLC layer createspackets which are provided to the layer below, i.e. the MAC layer. Thepackets provided by RLC to the MAC layer are RLC PDUs from an RLC pointof view and MAC SDUs from a MAC point of view. At the receiving side,the process is reversed, with each layer passing SDUs up to the layerabove, where they are received as PDUs.

While the physical layer essentially provides a bitpipe, protected byturbo-coding and a cyclic redundancy check (CRC), the link-layerprotocols enhance the service to upper layers by increased reliability,security and integrity. In addition, the link layer is responsible forthe multi-user medium access and scheduling. One of the main challengesfor the LTE link-layer design is to provide the required reliabilitylevels and delays for Internet Protocol (IP) data flows with their widerange of different services and data rates. In particular, the protocolover-head must scale. For example, it is widely assumed that voice overIP (VoIP) flows can tolerate delays on the order of 100 ms and packetlosses of up to 1 percent. On the other hand, it is well-known that TCPfile downloads perform better over links with low bandwidth-delayproducts. Consequently, downloads at very high data rates (e.g., 100Mb/s) require even lower delays and, in addition, are more sensitive toIP packet losses than VoIP traffic.

Overall, this is achieved by the three sublayers of the LTE link layerthat are partly intertwined. The Packet Data Convergence Protocol (PDCP)sublayer is responsible mainly for IP header compression and ciphering.In addition, it supports lossless mobility in case of inter-eNBhandovers and provides integrity protection to higher layer-controlprotocols. The radio link control (RLC) sublayer comprises mainly ARQfunctionality and supports data segmentation and concatenation. Thelatter two minimize the protocol overhead independent of the data rate.Finally, the medium access control (MAC) sublayer provides HARQ and isresponsible for the functionality that is required for medium access,such as scheduling operation and random access.

In particular, the Medium Access Control (MAC) layer is the lowestsublayer in the Layer 2 architecture of the LTE radio protocol stack andis defined by e.g. the 3GPP technical standard TS 36.321, currentversion 13.0.0. The connection to the physical layer below is throughtransport channels, and the connection to the RLC layer above is throughlogical channels. The MAC layer therefore performs multiplexing anddemultiplexing between logical channels and transport channels: the MAClayer in the transmitting side constructs MAC PDUs, known as transportblocks, from MAC SDUs received through logical channels, and the MAClayer in the receiving side recovers MAC SDUs from MAC PDUs receivedthrough transport channels.

The MAC layer provides a data transfer service (see subclauses 5.4 and5.3 of TS 36.321) for the RLC layer through logical channels, which areeither control logical channels which carry control data (e.g. RRCsignaling) or traffic logical channels which carry user plane data. Onthe other hand, the data from the MAC layer is exchanged with thephysical layer through transport channels, which are classified asdownlink or uplink. Data is multiplexed into transport channelsdepending on how it is transmitted over the air.

The Physical layer is responsible for the actual transmission of dataand control information via the air interface, i.e. the Physical Layercarries all information from the MAC transport channels over the airinterface on the transmission side. Some of the important functionsperformed by the Physical layer include coding and modulation, linkadaptation (AMC), power control, cell search (for initialsynchronization and handover purposes) and other measurements (insidethe LTE system and between systems) for the RRC layer. The Physicallayer performs transmissions based on transmission parameters, such asthe modulation scheme, the coding rate (i.e. the modulation and codingscheme, MCS), the number of physical resource blocks etc. Moreinformation on the functioning of the physical layer can be found in the3GPP technical standard 36.213 current version 13.0.0.

The Radio Resource Control (RRC) layer controls communication between aUE and an eNB at the radio interface and the mobility of a UE movingacross several cells. The RRC protocol also supports the transfer of NASinformation. For UEs in RRC_IDLE, RRC supports notification from thenetwork of incoming calls. RRC connection control covers all proceduresrelated to the establishment, modification and release of an RRCconnection, including paging, measurement configuration and reporting,radio resource configuration, initial security activation, andestablishment of Signalling Radio Bearer (SRBs) and of radio bearerscarrying user data (Data Radio Bearers, DRBs).

The radio link control (RLC) sublayer comprises mainly ARQ functionalityand supports data segmentation and concatenation, i.e. RLC layerperforms framing of RLC SDUs to put them into the size indicated by theMAC layer. The latter two minimize the protocol overhead independentlyfrom the data rate. The RLC layer is connected to the MAC layer vialogical channels. Each logical channel transports different types oftraffic. The layer above RLC layer is typically the PDCP layer, but insome cases it is the RRC layer, i.e. RRC messages transmitted on thelogical channels BCCH (Broadcast Control Channel), PCCH (Paging ControlChannel) and CCCH (Common Control Channel) do not require securityprotection and thus go directly to the RLC layer, bypassing the PDCPlayer.

RLC Retransmission Protocol

When the RLC is configured to request retransmission of missing PDUs, itis said to be operating in Acknowledged Mode (AM). This is similar tothe corresponding mechanism used in WCDMA/HSPA. Overall, there are threeoperational modes for RLC: Transparent Mode (TM), Unacknowledged Mode(UM), and Acknowledged Mode (AM). Each RLC entity is configured by RRCto operate in one of these modes.

In Transparent Mode no protocol overhead is added to RLC SDUs receivedfrom higher layer. In special cases, transmission with limitedsegmentation/reassembly capability can be accomplished. It has to benegotiated in the radio bearer setup procedure, whethersegmentation/reassembly is used. The transparent mode is e.g. used forvery delay-sensitive services like speech.

In Unacknowledged Mode data delivery is not guaranteed since noretransmission protocol is used. The PDU structure includes sequencenumbers for integrity observations in higher layers. Based on the RLCsequence number, the receiving UM RLC entity can perform reordering ofthe received RLC PDUs. Segmentation and concatenation are provided bymeans of header fields added to the data. The RLC entity inUnacknowledged mode is unidirectional, since there are no associationsdefined between uplink and downlink. If erroneous data is received, thecorresponding PDUs are discarded or marked depending on theconfiguration. In the transmitter, the RLC SDUs which are nottransmitted within a certain time specified by a timer are discarded andremoved from the transmission buffer. The RLC SDUs, received from higherlayer, are segmented/concatenated into RLC PDUs on sender side. Onreceiver side, reassembly is performed correspondingly. Theunacknowledged mode is used for services where error-free delivery is ofless importance compared to short delivery time, for example, forcertain RRC signaling procedures, a cell broadcast service such as MBMSand voice over IP (VoIP).

In Acknowledged Mode the RLC layer supports error correction by means ofan Automatic Repeat Request (ARQ) protocol, and is typically used forIP-based services such as file transfer where error-free data deliveryis of primary interest. RLC retransmissions are for example based on RLCstatus reports, i.e. ACK/NACK, received from the peer RLC receivingentity. The acknowledged mode is designed for a reliable transport ofpacket data through retransmission in the presence of high air-interfacebit error rates. In case of erroneous or lost PDUs, retransmission isconducted by the sender upon reception of an RLC status report from thereceiver.

ARQ is used as a retransmission scheme for retransmission of erroneousor missed PDUs. For instance, by monitoring the incoming sequencenumbers, the receiving RLC entity can identify missing PDUs. Then, anRLC status report can be generated at the receiving RLC side, and fedback to the transmitting RLC entity, requesting retransmission ofmissing or unsuccessfully decoded PDUs. The RLC status report can alsobe polled by the transmitter, i.e. the polling function is used by theRLC transmitter to obtain a status report from RLC receiver so as toinform the RLC transmitter of the reception buffer status. The statusreport provides positive acknowledgements (ACK) or negativeacknowledgment information (HACK) on RLC Data PDUs or portions of them,up to the last RLC Data PDU whose HARQ reordering is complete. The RLCreceiver triggers a status report if a PDU with the polling field set to‘1’ or when an RLC Data PDU is detected as missing. There are certaintriggers defined in subclause 5.2.3 of 3GPP TS 36.322, current version13.0.0, which trigger a poll for an RLC status report in the RLCtransmitter. In the transmitter, transmission is only allowed for thePDUs within the transmission window, and the transmission window is onlyupdated by the RLC status report. Therefore, if the RLC status report isdelayed, the transmission window cannot be advanced and the transmissionmight get stuck. The receiver sends the RLC status report to the senderwhen triggered.

Layer 1/Layer 2 Control Signaling

In order to inform the scheduled users about their allocation status,transport format, and other transmission-related information (e.g. HARQinformation, transmit power control (TPC) commands), L1/L2 controlsignaling is transmitted on the downlink along with the data. L1/L2control signaling is multiplexed with the downlink data in a subframe,assuming that the user allocation can change from subframe to subframe.It should be noted that user allocation might also be performed on a TTI(Transmission Time Interval) basis, where the TTI length can be amultiple of the subframes. The TTI length may be fixed in a service areafor all users, may be different for different users, or may even bydynamic for each user. Generally, the L1/2 control signaling needs onlyto be transmitted once per TTI. Without loss of generality, thefollowing assumes that a TTI is equivalent to one subframe.

The L1/L2 control signaling is transmitted on the Physical DownlinkControl Channel (PDCCH). A PDCCH carries a message as a Downlink ControlInformation (DCI), which in most cases includes resource assignments andother control information for a mobile terminal or groups of UEs.Several PDCCHs can be transmitted in one subframe.

Generally, the information sent in the L1/L2 control signaling forassigning uplink or downlink radio resources (particularly LTE(-A)Release 10) can be categorized to the following items:

User identity, indicating the user that is allocated. This is typicallyincluded in the checksum by masking the CRC with the user identity;

Resource allocation information, indicating the resources (e.g. ResourceBlocks, RBs) on which a user is allocated. Alternatively, thisinformation is termed resource block assignment (RBA). Note, that thenumber of RBs on which a user is allocated can be dynamic;

Carrier indicator, which is used if a control channel transmitted on afirst carrier assigns resources that concern a second carrier, i.e.resources on a second carrier or resources related to a second carrier;(cross carrier scheduling);

Modulation and coding scheme that determines the employed modulationscheme and coding rate;

HARQ information, such as a new data indicator (NDI) and/or a redundancyversion (RV) that is particularly useful in retransmissions of datapackets or parts thereof;

Power control commands to adjust the transmit power of the assigneduplink data or control information transmission;

Reference signal information such as the applied cyclic shift and/ororthogonal cover code index, which are to be employed for transmissionor reception of reference signals related to the assignment;

Uplink or downlink assignment index that is used to identify an order ofassignments, which is particularly useful in TDD systems;

Hopping information, e.g. an indication whether and how to applyresource hopping in order to increase the frequency diversity;

CSI request, which is used to trigger the transmission of channel stateinformation in an assigned resource; and

Multi-cluster information, which is a flag used to indicate and controlwhether the transmission occurs in a single cluster (contiguous set ofRBs) or in multiple clusters (at least two non-contiguous sets ofcontiguous RBs). Multi-cluster allocation has been introduced by 3GPPLTE-(A) Release 10.

It is to be noted that the above listing is non-exhaustive, and not allmentioned information items need to be present in each PDCCHtransmission depending on the DCI format that is used.

Downlink control information occurs in several formats that differ inoverall size and also in the information contained in their fields asmentioned above. The different DCI formats that are currently definedfor LTE are as follows and described in detail in 3GPP TS 36.212,“Multiplexing and channel coding”, section 5.3.3.1 (current versionv13.0.0 available at http://www.3gpp.org). For instance, the followingDCI Formats can be used to carry a resource grant for the uplink.

Format 0: DCI Format 0 is used for the transmission of resource grantsfor the PUSCH, using single-antenna port transmissions in uplinktransmission mode 1 or 2.

Format 4: DCI format 4 is used for the scheduling of the PUSCH, usingclosed-loop spatial multiplexing transmissions in uplink transmissionmode 2.

Uplink Access scheme for LTE

The uplink scheme allows for both scheduled access, i.e. controlled byeNB, and contention-based access.

In case of scheduled access, the UE is allocated a certain frequencyresource for a certain time (i.e. a time/frequency resource) for uplinkdata transmission. However, some time/frequency resources can beallocated for contention-based access. Within these time/frequencyresources, UEs can transmit without first being scheduled. One scenariowhere UE is making a contention-based access is for example the randomaccess, i.e. when UE is performing initial access to a cell or forrequesting uplink resources.

For the scheduled access, the Node B scheduler assigns a user a uniquefrequency/time resource for uplink data transmission. More specificallythe scheduler determines which UE(s) is (are) allowed to transmit, inwhich physical channel resources (frequency), and the correspondingtransport format to be used by the mobile terminal for the transmission.

The allocation information is signaled to the UE via the schedulinggrant, sent on the L1/L2 control channel. The scheduling grant messagecontains information which part of the frequency band the UE is allowedto use, the validity period of the grant, and the transport format theUE has to use for the upcoming uplink transmission. The shortestvalidity period is one sub-frame. Additional information may also beincluded in the grant message, depending on the selected scheme. Only“per UE” grants are used to grant the right to transmit on the UL-SCH(i.e. there are no “per UE per RB” grants). Therefore, the UE needs todistribute the allocated resources among the radio bearers according tosome rules. Unlike in HSUPA, there is no UE based transport formatselection. The eNB decides the transport format based on someinformation, e.g. channel quality feedback, reported schedulinginformation and QoS info, and the UE has to follow the selectedtransport format.

The usual mode of scheduling is dynamic scheduling, by means of downlinkassignment messages for the allocation of downlink transmissionresources and uplink grant messages for the allocation of uplinktransmission resources; these are usually valid for specific singlesubframes. They are transmitted on the PDCCH using the C-RNTI of the UE.Dynamic scheduling is efficient for services types in which the trafficis bursty and dynamic in rate, such as TCP.

In addition to the dynamic scheduling, a persistent scheduling isdefined, which enables radio resources to be semi-statically configuredand allocated to a UE for a longer time period than one subframe, thusavoiding the need for specific downlink assignment messages or uplinkgrant messages over the PDCCH for each subframe. Persistent schedulingis useful for services such as VoIP for which the data packets aresmall, periodic and semi-static in size. Thus, the overhead of the PDCCHis significantly reduced compared to the case of dynamic scheduling.

Logical Channel Prioritization, LCP, procedure

For the uplink the process by which a UE creates a MAC PDU to transmitusing the allocated radio resources is fully standardized; this isdesigned to ensure that the UE satisfies the QoS of each configuredradio bearer in a way which is optimal and consistent between differentUE implementations. Based on the uplink transmission resource grantmessage signaled on the PDCCH, the UE has to decide on the amount ofdata for each logical channel to be included in the new MAC and, ifnecessary, also to allocate space for a MAC Control Element.

In constructing a MAC PDU with data from multiple logical channels, thesimplest and most intuitive method is the absolute priority-basedmethod, where the MAC PDU space is allocated to logical channels indecreasing order of logical channel priority. This is, data from thehighest priority logical channel are served first in the MAC PDU,followed by data from the next highest priority logical channel,continuing until the MAC PDU space runs out. Although the absolutepriority-based method is quite simple in terms of UE implementation, itsometimes leads to starvation of data from low-priority logicalchannels. Starvation means that the data from the low-priority logicalchannels cannot be transmitted because the data from high-prioritylogical channels take up all the MAC PDU space.

In LTE, a Prioritized Bit Rate (PBR) is defined for each logicalchannel, in order to transmit data in order of importance but also toavoid starvation of data with lower priority. The PBR is the minimumdata rate guaranteed for the logical channel. Even if the logicalchannel has low priority, at least a small amount of MAC PDU space isallocated to guarantee the PBR. Thus, the starvation problem can beavoided by using the PBR.

Constructing a MAC PDU with PBR consists of two rounds. In the firstround, each logical channel is served in decreasing order of logicalchannel priority, but the amount of data from each logical channelincluded in the MAC PDU is initially limited to the amount correspondingto the configured PBR value of the logical channel. After all logicalchannels have been served up to their PBR values, if there is room leftin the MAC PDU, the second round is performed. In the second round, eachlogical channel is served again in decreasing order of priority. Themajor difference for the second round compared to the first round isthat each logical channel of lower priority can be allocated with MACPDU space only if all logical channels of higher priority have no moredata to transmit.

A MAC PDU may include not only the MAC SDUs from each configured logicalchannel but also a MAC CE. Except for a Padding BSR, the MAC CE has ahigher priority than a MAC SDU from the logical channels because itcontrols the operation of the MAC layer. Thus, when a MAC PDU iscomposed, the MAC CE, if it exists, is the first to be included, and theremaining space is used for MAC SDUs from the logical channels. Then, ifadditional space is left and it is large enough to include a BSR, aPadding BSR is triggered and included in the MAC PDU.

The Logical Channel Prioritization is standardized e.g. in 3GPP TS36.321 (latest version v12.4.0) in subclause 5.4.3.1. It is up to the UEimplementation to decide in which MAC PDU a MAC control element isincluded when the UE is requested to transmit multiple MAC PDUs in oneTTI.

Buffer Status Reporting

Buffer status reports (BSR) from the UE to the eNodeB are used to assistthe eNodeB in allocating uplink resources, i.e. uplink scheduling. Forthe downlink case, the eNB scheduler is obviously aware of the amount ofdata to be delivered to each UE; however, for the uplink direction,since scheduling decisions are done at the eNB and the buffer for thedata is in the UE, BSRs have to be sent from the UE to the eNB in orderto indicate the amount of data that needs to be transmitted over theUL-SCH.

Buffer Status Report MAC control elements for LTE consist of either: along BSR (with four buffer size fields corresponding to LCG IDs #0-3) ora short BSR (with one LCG ID field and one corresponding buffer sizefield). The buffer size field indicates the total amount of dataavailable across all logical channels of a logical channel group, and isindicated in number of bytes encoded as an index of different buffersize levels (see also 3GPP TS 36.321 v 12.4.0 Chapter 6.1.3.1).

Which one of either the short or the long BSR is transmitted by the UEdepends on the available transmission resources in a transport block, onhow many groups of logical channels have non-empty buffers and onwhether a specific event is triggered at the UE. The long BSR reportsthe amount of data for four logical channel groups, whereas the shortBSR indicates the amount of data buffered for only the highest logicalchannel group.

The reason for introducing the logical channel group concept is thateven though the UE may have more than four logical channels configured,reporting the buffer status for each individual logical channel wouldcause too much signaling overhead. Therefore, the eNB assigns eachlogical channel to a logical channel group; preferably, logical channelswith same/similar QoS requirements should be allocated within the samelogical channel group.

If the UE has no uplink resources allocated for including a BSR in thetransport block when a BSR is triggered, the UE sends a schedulingrequest (SR) to the eNodeB so as to be allocated with uplink resourcesto transmit the BSR. Either a single-bit scheduling request is sent overthe Physical Uplink Control Channel (PUCCH) (dedicated schedulingrequest, D-SR), or the random access procedure (RACH) is performed torequest an allocation of an uplink radio resource for sending a BSR.

SUMMARY

As NR is targeting for very high data rates, the processing timeavailable for both transmitter and receiver might be very limitedcompared with the amount of data to be transmitted. One example tominimize transmitter processing time is to minimize the needed real-timeprocessing. For instance, in the LTE, a PDCP PDU can be generated once aPDCP SDU (i.e. an IP packet) is available, i.e. PDCP PDU generation canbe done in a non-real-time manner, i.e. irrespectively of whether or notthere are currently resources granted for the PDCP PDU. However RLC andMAC PDUs can only be generated in real-time manner (i.e. after receptionof the UL grant). Segmentation, concatenation and multiplexing arerequired for DL UL data SDUs to fit within the total size of assigned TBsize determined by scheduler. Concatenation and segmentation requiresknowledge of the scheduling decision/grant size before it can beperformed so it is subject to strict real time processing requirements.This also implies that the transmitter cannot do any pre-processing foreither the RLC or the MAC layer, e.g., of sub-headers/headers before thescheduling/grant information. The inability to perform “pre-processing”incurs a processing delay upon grant reception. If the RLC and to someextent MAC processing could be completed beforehand (the grantreception); then the delay in MAC TB submission to PHY layer would be,comparatively, much smaller.

Moreover, one of the design goals for the U-Plane protocol architectureis to reduce the Layer-2 protocol overhead. In current LTE protocolarchitecture, the Length field is included twice, once in RLC and oncein MAC, which increases header overhead. Additionally, PDCP and RLC usetheir own sequence numbers in the existing LTE protocol architecture,which also increases header overhead.

One non-limiting and exemplary embodiment provides an approach improvingthe efficiency of the layer processing.

This is achieved by the features of the independent claims.

Advantageous embodiments are subject matter of the dependent claims.

In one general aspect, the techniques disclosed here feature a datatransmitting node that is provided for transmitting data over a wirelessinterface in a communication system to a data receiving node, the datatransmitting node comprising: a third layer processing unit forperforming an automatic repeat request, ARQ, retransmission according toa status report fed back from the data receiving node and forre-segmenting or not data to be retransmitted based on segment lengthinformation included in the status report including adding to the data asegmentation control information; a second layer processing unit forreceiving, from the third layer processing unit, a third layer dataunit, segmenting the third layer data unit based on a resourceallocation and forming a plurality of second layer data units includingthe respective segments of the third layer data unit and thesegmentation control information which is modified if re-segmentation isto be applied; and a first layer processing unit for receiving from thesecond layer one or more of the plurality of the second layer data unitsand mapping the one or more of the plurality of the second layer dataunits onto the resources allocated for data transmission.

It should be noted that general or specific embodiments may beimplemented as a system, a method, an integrated circuit, a computerprogram, a storage medium, or any selective combination thereof.

Additional benefits and advantages of the disclosed embodiments willbecome apparent from the specification and drawings. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the specification and drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following exemplary embodiments are described in more detail withreference to the attached figures and drawings.

FIG. 1 shows an exemplary architecture of a 3GPP LTE system;

FIG. 2 shows an exemplary overview of the overall E-UTRAN architectureof 3GPP LTE;

FIG. 3A illustrates the OSI model with the different layers forcommunication;

FIG. 3B illustrates the relationship of a protocol data unit (PDU) and aservice data unit (SDU) as well as the inter-layer exchange of same;

FIG. 4 gives an overview of the different functions in the PDCP, RLC andMAC layers as well as illustrates exemplary the processing of SDUs/PDUsby the various layers;

FIG. 5A is a schematic drawing illustrating processing of data bydifferent layers of the radio access network in LTE user plane;

FIG. 5B is a schematic drawing illustrating pre-processing of MAC-PDUsand their mapping onto physical resources by modifying the preprocessedheaders;

FIG. 6 is a schematic drawing of an exemplary transmission sideprocessing by three layers;

FIG. 7 is a schematic drawing of an exemplary reception side processingby the three layers in case one of two MAC PDUs is lost;

FIG. 8 is a schematic drawing of an exemplary transmission sideprocessing by the three layers in case one of two MAC PDUs is lost;

FIG. 9 is a schematic drawing of an exemplary reception side processingby the three layers in case both MAC PDUs are correctly received;

FIG. 10 is a schematic drawing showing an exemplary layer processing atthe transmitter side for a first transmission;

FIG. 11A shows a status report (STATUS PDU) as defined in the 3 GPP TS36.322;

FIG. 11B is a schematic drawing illustrating an exemplary format of anRLC status report;

FIG. 12 is a schematic drawing showing an exemplary layer processing atthe transmitter side for a first transmission using segment numbers;

FIG. 13 is a schematic drawing showing an exemplary layer processing atthe receiver side for the first transmission using segment numbers;

FIG. 14 is a schematic drawing showing an exemplary layer processing atthe transmitter side for a retransmission using (re)segment numbers;

FIG. 15 is a schematic drawing showing an exemplary layer processing atthe receiver side for the retransmission using (re)segment numbers;

FIG. 16 is a schematic drawing showing an exemplary layer processing atthe transmitter side for a first transmission supportingmulti-connection;

FIG. 17 is a schematic drawing showing an exemplary layer processing atthe receiver side for the first transmission supportingmulti-connection;

FIG. 18 is a schematic drawing showing an exemplary layer processing atthe transmitter side for a retransmission supporting multi-connection;

FIG. 19 is a schematic drawing showing an exemplary layer processing atthe receiver side for the retransmission supporting multi-connection;

FIG. 20 is a block diagram illustrating functional structure ofexemplary data transmitting and data receiving apparatuses; and

FIG. 21 is a flow diagram illustrating steps of exemplary methodsperformed at the transmitting and receiving side.

DETAILED DESCRIPTION

Basis of the Present Disclosure

L1/L2 Processing

FIG. 4 exemplary depicts the data flow of an IP packet through thelink-layer protocols down to the physical layer. The figure shows thateach protocol sublayer adds its own protocol header to the data units aswell as the mapping of the transport block on a subframe. Transportblock (TB) denotes the MAC PDU which is mapped onto the physical layer.

The mapping of the transport block onto the subframe in LTE is performedwithin a so-called transmission time interval (TTI). Generally a singletransport block is mapped in one TTI to one subframe in case of singleinput single output (SW), i.e. transmitter and receiver operating withone antenna. In case of MIMO/MISO (multiple input multipleoutput/multiple input single output), two codewords corresponding to twotransport blocks may be mapped in one TTI to the physical resources. Ingeneral, more than two transport blocks may be considered for mapping.

The LTE L2 functions are summarized in the following table.

TABLE 1 Table 1: LTE L2 functions (Tx side) UP Protocol layer FunctionsPDCP Bearer mapping (EPS bearer−> radio bearer) Sequence numberingHeader compression Security Routing RLC Sequence numbering SegmentationConcatenation ARQ MAC Scheduling Multiplexing HARQ

In LTE, the RLC layer performs concatenation/segmentation of PDCP PDUs.

When the transmitter knows the transport block (TB) size, the MAC layerperforms logical channel prioritization (LCP) to determine how much dataeach RLC-entity should transmit (provide to the lower layers, i.e. tothe MAC/PHY). Each RLC entity provides one RLC PDU containing one ormore RLC SDUs. For each RLC SDU ending in the RLC PDU, a correspondingL-field (length field) is added, which enables the receiver to extractthe corresponding SDUs. If the last contained RLC SDU does not fitentirely into the RLC PDU, it is segmented, i.e., the remainder of theRLC SDU will be sent in the subsequent RLC PDU(s). Whether the first(last) byte of the RLC PDU corresponds to the first (last) byte of theRLC SDU is indicated by the “Framing Info” flags (2 bit) located in theRLC header. Other than that, segmentation does not any additionaloverhead. In order to re-establish the original order of the data and todetect losses, the RLC sequence number (SN) is added to the RLC PDUheader.

MAC multiplexes the RLC PDUs for different logical channel identifiers(LCIDs) and adds a corresponding sub-header with the LCID and theL-field. A high level illustration of the transport block structure isillustrated in FIG. 4. Recently, the 3GPP has started to study and workon the 5^(th) generation system under the name new radio (NR). NRtargets very high data rates (currently up to 20 Gbit/sec in downlinkand 10 Gbit/sec in uplink).

Detailed Description of Present Disclosure

A mobile station or mobile node or user terminal or user equipment (UE)is a physical entity within a communication network. One node may haveseveral functional entities. A functional entity refers to a software orhardware module that implements and/or offers a predetermined set offunctions to other functional entities of a node or the network. Nodesmay have one or more interfaces that attach the node to a communicationfacility or medium over which nodes can communicate. Similarly, anetwork entity may have a logical interface attaching the functionalentity to a communication facility or medium over which it maycommunicate with other functional entities or correspondent nodes.

The terms “radio resources” as used in the set of claims and in theapplication is to be broadly understood as referring to physical radioresources, such as time-frequency radio resources.

The following exemplary embodiments provide an improved radio interfacelayer processing for the new radio technology envisioned for the 5Gmobile communication systems. As yet, very few details have been agreedon with regard to the 5G mobile communication system, such that manyassumptions have to be made in the following in order to be able toexplain the principles underlying the embodiments. These assumptions arehowever to be understood as merely examples that should not limit thescope of the disclosure. A skilled person will be aware that theprinciples of the present disclosure as laid out in the claims can beapplied to different scenarios and in ways that are not explicitlydescribed herein. For example, the new radio technology will be evolvingfrom the radio technology already defined for LTE(-A), although severalchanges can be expected so as to meet the requirements for 5G mobilecommunication systems. Consequently, particular exemplaryimplementations of the various embodiments could still reuse procedures,messages, functions etc. already defined for the LTE(-A) communicationsystems (according to Release 10/11/12/13/14 etc.) as long as they areequally applicable to both the new radio technology for 5G communicationsystems and to the various implementations as explained for thefollowing embodiments.

According to the present disclosure, the concatenation/segmentationfunctionality is moved from the RLC layer to the MAC entity. Thisapproach provides some advantages, for instance, the RLC PDUs and partlythe MAC PDUs can be pre-constructed at the terminal (if the transmissionis performed in the uplink), before an UL grant is received. Thisreduces processing time through pre-constructing the respective RLC PDUand partly MAC PDU. The RLC layer does not have to wait for MACscheduling decision and the RLC PDU size indication (both carried withresource allocation by L1/L2 signaling). This reduces the processingtime in generating the transport block.

FIG. 5A shows the main functions of protocol layers on the transmitter(TX) and the receiver (RX) sides. As can be seen, at the transmitterside, the segmentation is performed in MAC layer, in cooperation of theRLC layer.

FIG. 5B illustrates basic operation performed on the transmitter side:

a) The RLC and/or MAC PDUs are pre-processed on a per PDCP PDU basis,i.e. the RLC layer does not concatenate the PDCP PDUs. However, the RLClayer may further segment the RLC SDU (PDCP PDU), which is illustratedby two results of a PDCP PDU segmenting, namely R1-PDU1 and R2-PDU2.Pre-processing could be based on a “minimal (or alternatively, anaverage) grant size” which is statistically available, with certain highconfidence level, in a given radio condition (e.g. RSSI/RSRP etc.). So,a pseudo LCP (since it works with estimated grant sizes) is run on thisminimal or an average grant size and the RLC and MAC PDUs arepre-processed accordingly. When the (real) grant is received and the LCPhas been run in the MAC layer, some of the pre-processed RLC PDUs, whichcan be accommodated in the granted resources (i.e. size of thecorresponding MAC PDU is smaller or equal to the grant size for thecorresponding LCID) based on the result of the LCP, will be submitted tothe physical layer. The physical layer may initiate its processing onthese immediately, i.e. in the time instance t1. In FIG. 5B, thepre-segmented R1-PDU1 and R2-PDU1 which have appended the pre-processedMAC header can be accommodated in the granted resources.

b) The pre-segmented R1-PDU2 and R2-PDU2 cannot be accommodated in aswhole to the grated resources and thus, further segmentation of thesePDUs is necessary with the knowledge of the allocation size and afterthe LCP has been performed. In other words, the remaining grant (afterthe above step) would require the pre-processed PDUs to be segmented andtheir corresponding headers need to be recomputed. The segmentation canbe done in the MAC layer (on the RLC PDUs which were alreadypre-processed and submitted to it) or in the RLC layer (RLC re-computingthe header after the segmentation based on result of LCP). After this L2processing, the resulting part(s) (segments) of the MAC PDU aresubmitted to the physical layer. The physical layer may initiate itsprocessing on these subsequently (i.e. at the time instance t2).

In FIG. 5B, the two different RLC entities belong to different logicalchannels. Accordingly, MAC also decides, based on logical channelprioritization procedure (LCP), which of the corresponding MAC PDUs areto be provided to the physical layer at which time point. One example ofa LCP procedure is known from the LTE and referred to above in thebackground section. Nevertheless, the present disclosure is not limitedthereto and in general.

At the receiver side, after physical layer processing, the correspondingreverse steps are performed:

a) The MAC layer performs the de-multiplexing on the basis of the MACheader (basically the LCID field and the Length field) and gives theresulting MAC SDU(s) to the RLC. When the MAC layer passes the MAC SDUto the RLC layer, it also keeps segmentation/concatenation header fieldsince segmentation and concatenation are done by MAC and re-ordering andre-assembly of segments are performed by RLC. This is the reason why MACpasses segmentation header filed to RLC. In other words, the MAC layerpasses to the RLC not only MAC SDU, but also a part of the MAC headerrelated to segmentation/concatenation.

b) The RLC layer reassembles the RLC PDU segments (if any) beforeforwarding the complete RLC SDU(s) to PDCP. Submission of complete RLCSDUs to PDCP is done also out of order, i.e. including “holes” at theplace where a segment is missing for instance because it has not beencorrectly received within a predefined time or a predefined number ofretransmissions. However, the RLC needs to keep track of the missingPDU(s) and PDU segment(s). The ARQ runs at RLC, so that any missing RLCPDU and/or PDU segment shall be reported to the TX side for a possiblere-transmission. Here, the ARQ shall try to retrieve the missing RLC PDUand/or PDU segment until upon the expiry of a timer, Timer1. Timer1 isstarted when a hole first appears (or when the subsequent/next RLC SDUis delivered to the PDCP layer). Upon expiry of Timer1 RLC shall informthe PDCP layer as well as RRC. The RRC might take further actions liketriggering a Radio Link Failure (RLF) procedure. In general; end-to-endprotocols of higher layers like TCP may still take care of correctdelivery.

c) The PDCP layer shall decipher the incoming PDUs received from RLC onthe basis of PDCP SN (or COUNT, if available directly from the header;else; it needs to estimate/calculate COUNT from the SN included in thePDCP header). Calculation of COUNT will be done by adjusting the lastCOUNT value with the difference between the last PDCP SN and the PDCP SNvalue in the just received PDCP PDU header. Here, the “last” refers tothe previous PDCP PDU that was successfully deciphered. In addition,PDCP shall wait for the “hole(s)” to arrive from RLC. However, if theindication from RLC (upon Timer1 expiry) comes before the correspondingPDCP PDU is received, the PDCP SDUs are submitted to the upper layers(including holes).

The above approach is applicable not only to the AM, but also to UM. Inthe case that UM is applied, there are no retransmissions on the RLClayer. Nevertheless, at the receiver side, if a RLC PDU or a RLC PDUsegment is missing, the RLC SDU is still assembled and provided to thePDCP layer.

In the AM, when the RLC Status Report indicates that a RLC PDU and/orPDU segment is missing, the TX side RLC submits the correspondingmissing RLC PDU and/or PDU segment to the MAC layer including a suitableheader to assist the receiver in reassembly of the segment(s) byretransmitting it.

Alternatively, the RLC layer may submit the whole RLC PDU to the MAClayer, even if just a segment of the corresponding RLC PDU was indicatedas missing; in addition, the RLC layer shares the Status Report details(i.e, the entire status report) with the MAC layer. An advantage of thisapproach is to reduce RLC header overhead. If the re-segmentation isdone in the RLC layer, then the RLC layer adds segmentation headerfields which increases header overhead. To overcome this problem, thecomplete RLC PDU is sent to MAC and MAC performs segmentation based theon status report. The status report of RLC is understood by MAC sinceuniversal (common) sequence number is being used between the layers(PDCP, RLC, MAC). In this case, the MAC layer performs there-segmentation based on this knowledge and the result of the LCP, andincludes a suitable header to assist the receiver in reassembly of thesegment(s).

It is noted that the above description refers to the “MAC”, “RLC” and“PDCP”, which are terms employed in the UMTS/LTE(-A) standards. However,the present disclosure is not limited to these standards, or to theiradvancements and may work irrespectively of the used terminology.

In other words, the framework may be seen as a protocol stack in whichthere a first layer responsible for mapping/de-mapping of the dataonto/from the physical resources (corresponding to the physical layer),a second layer (corresponding to MAC) and a third layer (correspondingto RLC and/or PDCP). It is noted that the terms “first layer”, “secondlayer” and “third layer” here do not necessarily correspond to the OSImodel layers.

The reduction of protocol stack processing latency can be achieved in atransmitter side with a first, physical, layer; a second layer; and athird layer in that the second layer receives from the third layerpre-processed third layer PDUs (generated by the third layer withoutknowledge of the resource allocation) and receives (from the receiver inuplink or internally in downlink) resource allocation for the physicallayer. The pre-processed third layer PDUs may be added (already at thethird layer or at the second layer) a header including segmentationinformation. It is noted that such pre-processed third layer PDUs may beprovided for a plurality of third layer entities, corresponding to aplurality of logical channels which may have different priorities.Accordingly, the second layer then may perform a prioritizationprocedure. Based on the received resource allocation and possibly alsobased on the result of prioritization procedure, the second layer thenprovides the first layer with the suitable preprocessed third layer PDUsincluding the segmentation information as the second layer header at afirst time point t1 and possibly performs further segmentation of thepre-processed PDUs and modifies the segmentation information in theheader accordingly before providing the data to the first layer at atime point t2 later than the time point t1.

It is noted that the third layer PDUs received at the second layer maybe already pre-segmented according to ARQ status report if the thirdlayer implements ARQ. But this approach is also applicable if the thirdlayer does not implement ARQ. The pre-segmentation may then be donebased on some statistic measures of past allocations or according toanother rule or does not have to be performed at all.

Moreover, the present disclosure may also be advantageously applied todouble or multi-connectivity. Multi-Connectivity is a mode of operationwhereby a multiple Rx/Tx UE in the connected mode is configured toutilize radio resources amongst E-UTRA and NR provided by multipledistinct schedulers connected via a non-ideal backhaul. In other words,with multiple connectivity a layer above the third layer in thetransmitter (such as a terminal) provides the same packet (IP or PDCP)to be transmitted to multiple base stations (eNBs). The two or more basestations then receive the same packet independently, thus increasing theprobability of correct reception by the network.

The concept of multi-connectivity is somewhat similar to the dualconnectivity which is one promising solution under discussion in 3GPPRAN working groups is the so-called “dual connectivity” concept. Theterm “dual connectivity” is used to refer to an operation where a givenUE consumes radio resources provided by at least two different networknodes connected with non-ideal backhaul. Essentially, a UE is connectedwith both macro cell (macro eNB) and small cell (secondary eNB).Furthermore, each eNB involved in dual connectivity for a UE may assumedifferent roles. Those roles do not necessarily depend on the eNB'spower class and can vary among UEs. However, unlike dual connectivity,where different data are sent from a UE to different eNBs, inmulti-connectivity, the same IP/PDCP packet is transmitted over aplurality of links/cells. Among the multiple receiving eNBs, one isfunctioning as a master eNB, which implements the layer that performsthe reassembly of the segments received via multiple connections. Themaster eNB communicates with the other eNBs.

For instance, speaking in terms of LTE, the PDCP layer takes over thereassembly function in addition to other functions that it is alreadyperforming upon switching from single to multi connectivity. The ARQ maystill run at the RLC layer (in the AM) and in this case the PDCP layerwill need to share the missing (fully or partially) PDCP SN details withthe RLC layer. The PDCP layer will inform the RLC layer about missingpart of segments. Afterwards, the receiving entity of the RLC layer willsend status report to transmitting entity of the RLC layer. Therefore, aseparate ARQ in RLC and PDCP layer is not required, which means singleconnectivity and multi-connectivity, ARQ may both run in RLC layer.Alternatively, the PDCP layer can compose its own Status Report and sendit to the TX-PDCP entity. The Status Report shall contain information onthe missing PDCP PDUs and/or PDU segments.

In order to enable the latency reduction and/or overhead reduction asdescribed above, the present disclosure provides an efficient layermodel to be implemented at the transmitter and the receiver side. Thisincludes one or more of the following:

Moving the segmentation into the second layer, i.e. as close as possibleto the physical layer which must perform the real-time processing sinceit maps the data onto the physical resources (from the third layer).This provides the possibility of preparing data for transmission over ashared channel even before the corresponding grant is received (Theterminal implementation may make a use of this possibility or not. Inother words, whether or not the terminal timing makes use ofpre-processed PDUs may be left to the implementation).

Employing common control information accessed by multiple layers.

Usually, the layer model assumes that each layer only accesses controlinformation generated on that layer: This leads sometimes to overlappingduplicated control information being provided in several layers, i.e,headers of the different layers' PDU's. This may be the case for thesequence number which enables reordering of the received data. A commonsequence number may be used for more than one layer (such as PDCP andRLC) which reduces header overhead.

A higher layer (such as third layer or more particular RLC or PDCP)supports ARQ functionality. Therefore, based on the third-layer statusreport, the third layer performs the segmentation of PDUs, Here it isassumed that the segmentation of the third layer PDU based on the statusreport may differ from the segmentation performed on the basis of thereceived allocation performed in the lower layer (second layer or moreparticularly MAC). Similar advantage may be achieved if the third layerprovides the second layer with the segmenting information based on thestatus report and only the second layer performs the segmentation basedon both the allocation and the status report. This approach enablessaving both time (thanks to pre-processing) and resources(re-segmentation enables only retransmitting the missing segments).

Layer 2 Segmentation, Layer 3 Pre-Segmentation for ARQ

In accordance with an embodiment, a data transmitting node is providedfor transmitting data over a wireless interface in a communicationsystem to a data receiving node. In order to implement the functionalityof protocol stack layer model, the data transmitting node comprises athird layer processing unit for performing or not an ARQ retransmissionaccording to a status report fed back from the data receiving node andfor re-segmenting or not data to be retransmitted (if any) based onsegment length information included in the status report. There-segmentation includes adding to the segmented data segmentationcontrol information, for instance as a header. This header is alsoadvantageously interpreted and used in a second layer, provided to thesecond layer together with the third layer data unit. In this embodimentit is assumed that the retransmission protocol is handled by the thirdlayer, which does not exclude application of independent ARQ/HARQprotocols in other layers below or above the third layer.

The data transmitting node further comprises a second layer processingunit for receiving, from the third layer processing unit, a third layerdata unit, segmenting the third layer data unit based on a resourceallocation and forming a plurality of second layer data units includingthe respective segments of the third layer data unit and thesegmentation control information which is modified if re-segmentation isto be applied. The resource allocation may be either received from thedata receiving node or generated at the data transmitting node. Forinstance, if the transmitting node is terminal (UE), the resourceallocation (uplink grant) may be received from a base station, i.e. fromthe data receiving node. On the other hand, if the transmitting node isa base station, the resource allocation for the transmission may begenerated at the base station, and provided to the MAC layer. However,the present disclosure is also applicable to direct communicationbetween terminals or between relays and terminals or relays and basestations.

Finally, the data transmitting node comprises a first layer processingunit for receiving from the second layer one or more of the plurality ofthe second layer data units and mapping the one or more of the pluralityof the second layer data units onto the resources allocated for datatransmission.

It is noted that the data transmitting node may further comprise afourth layer processing unit for providing sequence number within itsheader. The sequence number is increased for each new fourth layer SDU,i.e. with each IP packet, the increasing may be cyclical while thesequence number has a predefined maximum value. The third layeradvantageously does not provide another sequence number but encapsulatesthe fourth layer processing unit including the sequence number providedby the PDCP layer.

In terms of LTE terminology, the first layer may be the physical layer;the second layer may be the MAC layer and the third layer may be the RLClayer, whereas the fourth layer may be the PDCP. However, it is notedthat the third layer may also be considered to be the PDCP layer in someembodiments or one combined layer with functions of both RLC and PDCPespecially in case of architectures evolving based from the present LTE.

FIG. 6 illustrates processing at a transmitter side according to thisembodiment and exemplified using LTE terminology. The transmitter sidemay be the terminal transmitting data in the uplink to a base station.However, the present disclosure is not limited thereto and thetransmitting side may be a terminal transmitting data to anotherterminal or to any other node. Moreover, the present disclosure may alsobe applied to a base station or a relay node or another node being thedata transmitter.

As shown in FIG. 6, an IP packet 1 with the length of 1200 bytes isprovided to the PDCP layer, thus forming a PDCP SDU. The PDCP SDU isadded a header including a D/C indicator which may be a single bit. Thisbit indicates whether the content of the PDCP PDU is a Data or ControlPDU. In this example, it is set (i.e. the bit is equal to 1) for dataPDU and unset (i.e. the bit is equal to 0) for control PDU. However, ingeneral, the setting/unsetting may be reversed. The PDCP header furtherincludes the PDCP sequence number (SN).

The PDCP PDU1 (with a payload of 1200 bytes) is sent to the RLC layer,thus forming an RLC SDU. The RLC layer includes the relevant RLC headerto the RLC PDU. As can be seen in the figure, the RLC header includesanother D/C flag, a P flag and an RF flag. The D/C flag indicateswhether control or data are carried by the RLC PDU, while the P flag isa polling bit which is set to request a status report from the receiver(peer RLC entity). If it is not set then a status report is notrequested. The RF flag is a re-segmentation flag indicating whether theRLC PDU is a complete PDCP PDU or a PDCP PDU segment. The RF value isinitially set to 0, indicating that the RLC PDU is a complete PDU, andthen delivered to the MAC layer as a part of the RLC PDU1. In thisexample, for the first transmission of data of the PDCP PDU/IP packet,the RLC layer does not perform segmentation; rather the MAC layerperforms the segmentation. Accordingly, for the first transmission, theRF value is always set to 0.

In the example of FIG. 6, the transmitting MAC entity needs to segmentthe RLC PDU based on the grant received. Further, the grant sizesassumed in this example are 800 and 400 bytes at two differenttransmission occasions (or at least one grant for 800 bytes and the restwaiting for another grant). Thus, the MAC layer segments the RLC PDUcorresponding to a MAC SDU. After the segmentation of the RLC PDU, thetransmitting MAC entity includes segmentation-relevant MAC headerportions into the respective MAC PDUs to indicate segment offset (SO)and last segment field (LSF) of the included RLC PDU and forms the MACPDUs which are referred as MAC PDU1 and MAC PDU2 in FIG. 6. MAC PDU1contains an 800 byte payload whereas MAC PDU2 contains a 400 bytepayload. MAC PDU1 and MAC PDU2 are sent to TTI0 and TTI1 respectively.The TTI0 and TTI1 are then multiplexed into different resources, forinstance different time resources. However, it is noted that this is notto limit the present disclosure to mapping the two MAC PDUs to differenttime points. More than one MAC PDU may be generally mapped ontodifferent type of resources, for instance different frequencies ordifferent streams of a MIMO system, orthogonal codes, or the like.

The SO field in this example indicates the position of the PDU segmentin bytes within the original PDU. Specifically, the SO field indicatesthe position within the data field of the original PDU to which thefirst byte of the data field of the PDU segment corresponds to. Thefirst byte in the data field of the original PDU is referred by the SOfield value zero. The LSF field indicates whether or not the last byteof the PDU segment corresponds to the last byte of a PDU.

The MAC layer may include into the MAC PDU1 and MAC PDU2 further fieldssuch as logical channel D (LCID) and an extension flag (E), whichindicates whether or not there are other fields following the MACheader. Value 1 indicates that there is at least one or more E/LCIDfields following this field. Value 0 indicates that there is no moreE/LCID fields following this field implying that the next byte is thestart byte of the MAC SDU. There may some further fields or reservedfields in the header (not shown in the figure).

According to this embodiment also a data receiving node for receivingdata over a wireless interface in a communication system from a datatransmitting node. The data receiving node comprises a first layerprocessing unit for de-mapping one or more of a plurality of secondlayer data units from the resources allocated for data transmission andfor providing the one or more of the plurality of the de-mapped secondlayer data units to a second layer processing unit. Moreover, the datareceiving node further comprises the second layer processing unit forperforming de-multiplexing of a plurality of third layer unit segmentsand segmentation control information from the one or more of theplurality of second layer data units, and forwarding the plurality ofthe demultiplexed third layer unit segments together with thesegmentation control information to a third layer processing unit. Thedata receiving node further comprises the third layer processing unitfor performing re-ordering of the plurality of the demultiplexed thirdlayer segments and assembly into a third layer unit.

Thus, the segmentation information which is a part of the second layerdata units (and may be, in particular carried in the second layerheader) is also looked at and used at the third layer. This approachdisregards thus the strict layer separation on one hand; on the otherhand it saves overhead and enables to efficiently perform there-ordering and re-assembly at the third layer. This is particularlyadvantageous if the ARQ procedure is implemented in the third layer,which—however—is not necessary and not limiting for the presentdisclosure.

According to an exemplary implementation, the third layer processingunit in the data receiving apparatus is further configured to generatecontrol data carrying a status report indicating whether or not at leastone third layer unit segment has been received correctly. The statusreport may include at least one of positive acknowledgements or negativeacknowledgements for at least one third layer data unit and/oridentification of correctly received or missing segments of the thirdlayer data unit. Exemplary format of the status report which may beemployed here can be found in 3GPP TS 36.322, Version 13.2.0, Section6.2.1.6. However; it is noted that this is only an example and thestatus report may have a different format and content as long as itenables positive and/or negative reception acknowledgement for a thirdlayer PDU or its segments.

FIG. 7 illustrates an exemplary reception processing of MAC PDU1 and MACPDU2 received over an error prone channel. As shown in FIG. 7, MAC PDU1is received (800 bytes payload) correctly but MAC PDU2 (400 bytespayload) is lost (could not been decoded correctly, i.e. the CRCfailed).

The MAC layer performs de-multiplexing of the RLC PDU1 and sends it toRLC layer. The RLC layer then performs reassembling and reordering ofthe MAC segments. The RLC receiving side (RX) sends status reportindicating correct reception of the 800 to 1200 bytes belonging to theMAC PDU1 to the RLC transmitting side (TX). The re-ordering andre-assembling of the RLC PDU segments is performed based on the headerinformation from the MAC layer. This includes in the example of FIG. 7in particular the segment offset and the LSF indicator. The RLC layerD/C field enables distinguishing between the RLC data PDUs and RLCcontrol PDUs such as status reports.

FIG. 8 shows the exemplary subsequent actions at the RLC transmittingside, assuming that the transmitter side is aware of the second missingMAC-PDU2 segment (for instance based on the status report). As shown inFIG. 8, in this example the RLC TX takes the complete RLC PDU of thecorresponding missing packet from the transmission buffer and performs anew segmentation (re-segmentation) of the 400 (800 to 1200) bytes whichare indicated by the RLC status report as missing. The re-segmentationincludes also attaching the appropriate RLC header. The RLC header hereincludes the segment offset which indicates the position of the RLC PDUsegment which is to be retransmitted by means of an offset in bytes. Inthis example, the segmentation offset SO=801 since the missing 400 bytesfrom 801 to 1200 are to be retransmitted. Then the re-segmented RLC PDUcorresponding to the missing 400 bytes is delivered to the MAC layer.

The MAC layer then performs segmentation of the received RLC PDU andforms MAC PDU1 (which contains 200 bytes of data) and MAC PDU2 (whichalso contains 200 bytes of data), which are then sent to TTI0 and TTI1respectively—as described above with reference to FIG. 6 for the firsttransmission. Of course, in general, the MAC layer only performssegmentation if it is required. Here in this example, the grant size isnot sufficient and that is why the MAC layer forms MAC PDU1 and MACPDU2. If the allocation is sufficient, no segmentation is needed, orpossibly, concatenation is performed (in case the allocation is largerthan needed for one MAC PDU).

In particular, the MAC layer reads the SO field and the LSF field fromthe RLC header and modifies them on the basis of the grant size, i.e. inthis example to reflect the segmentation size of 200 bytes and 200bytes, respectively. As can be seen in FIG. 8, the MAC layer providesthe new segmentation information in the respective headers of thesegmented MAC PDUs, namely SO=801 and SO=1001, corresponding to theposition of the new segments of data to be retransmitted within thefirst-transmitted (not re-segmented) RLC PDU and the LSF. FIG. 9illustrates an example in which the MAC PDU1 and MAC PDU2 from FIG. 8are both received correctly. The MAC layer delivers the correctlyreceived MAC PDU1 and MAC PDU2 to the RLC layer. The RLC layer performsthe reordering and reassembling of MAC segments and then delivers thecomplete PDCP PDU to the PDCP layer. The reordering is performed basedon the sequence numbers (SN). As mentioned above, a single sequencenumber is advantageously used for both PDCP and RLC layers in order tosave overhead.

In other words, the RLC RX collects all segments of the RLC PDU(retransmitted or correctly received after the first transmission),re-orders them based on the MAC header information and reassembles theRLC PDU. The reassembled PDU may then be provided to the higher layers(such as PDCP or directly IP, if there is no PDCP) for furtherprocessing.

Accordingly, the present disclosure modifies the functions performed bythe different layers of the RAN protocol stack as is illustrated inTable 2 below.

TABLE 2 Table 2: NR protocol stack tasks UP protocol layer FunctionsPDCP TX Header compression SN attached Ciphering Retransmission RLC TXDelivering packets to MAC layer Packet (re)-segmentation onretransmission MAC TX Concatenation/multiplexing Segmentation HARQtransmission MAC RX HARQ reception De-multiplexing RLC RX MAC segmentreordering/status reporting (Retransmission) Packet reassembly Out ofsequence delivery to PDCP PDCP RX Packet deciphering Complete PDU basedreordering/status reporting Header decompression

In the following Tables 3-5 provide examples of the headers of therespective layers PDCP, RLC and MAC.

TABLE 3 Table 3: The description of the PDCP header fields Data/Centralbit D/C indicates whether PDU is data or control PDU (D/C) Sequencenumber 10 bit sequence number (SN)

TABLE 4 Table 4: The description of the RLC header fields Data/ControlD/C indicates whether PDU is data or control PDU bit (D/C)Re-segmentetion RF indicates whether PDU is complete or segment flag(RF) PDU. Polling bit (P) The P field indicates whether or not thetransmitting side of an AM RLC entity requests a STATUS report from itspeer.

TABLE 5 Table 5: The description of the MAC header fields Length The LIheld indicates the length in bytes of the indicator corresponding Datafield element present the MAC data (LI) PDU delivered/received by MACentity. Extension The E field indicates whether this field is the end ofthe bit (E) header or another extension follows or not. Segmentation TheSO field indicates the start position of the first byte offset (SO) ofthe corresponding MAC SDU in bytes. Last segment The LSF is set to 1 toindicate that this is the last field (LSF) segment of the RLC PDU.

In the above tables; the length of the sequence number is exemplified as10 bits. However; it is noted that this is only an example which is notto limit the present disclosure. Already in LTE, the length of the PDCPsequence number can be 5 bit, 7 bits or 12 bits depending on the radiobearer's characteristics. The length of the sequence number is a matterof system design as is clear to those skilled in the art any may beselected to have any length for the purposes of the present disclosure.

As shown in FIG. 6, the PDCP PDUs are sent to the RLC layer at thereceiver. Advantageously, the PDCP, RLC and MAC layers use a universalsequence number which is understood by all these layers. In thisexample, the PDCP sequence number is used, which is understood by allthree layers, or at least the PDCP and RLC since the SN is notnecessarily needed in the lower layers.

The RLC layer includes the relevant RLC header in the RLC PDU, forinstance the RF field to indicate a complete or segmented PDU. The RFvalue is initially set to 0 and is updated when a status report arrivesat the RLC TX. When the transmitting side transmits the RLC data PDUs,it still stores the RLC PDUs in the retransmission buffer for possibleretransmission. A retransmission may be requested by the receiver bymeans of the status report. As can be seen in FIG. 6, the RLC PDUs arethen delivered to the MAC layer. Afterwards, the transmitting MAC entityperforms segmentation and/or concatenation on the MAC SDU received fromthe upper layer (RLC) to form the MAC PDU(s).

The size of the MAC PDU at each transmission opportunity (TTI) isdecided and notified by the MAC layer itself depending on the radiochannel conditions and transmission resources available therefor. Asmentioned in the background section, dynamic scheduling may be appliedfor the shared channel so that in each TTI a different allocation ispossible (capable of accommodating different amount of date for instancedue to varying modulation and coding scheme for better link adaptation).

The size of each transmitted MAC PDU can thus be different. Thetransmitting MAC entities include RLC PDUs/MAC SDUs into a MAC PDU inthe order, in which they arrive at the MAC entity. Therefore a singleMAC PDU can contain complete RLC PDUs or an RLC PDU segment since MACmay perform not only segmentation but also concatenation, depending onthe respective segment sizes and allocated resources. If a MAC PDUcontains N (N being an integer larger than 0) RLC PDUs and/or PDUsegments, then the MAC layer shall include N−1 Length fields (L-fields)for all respective corresponding RLC PDUs and/or PDU segments i.e. oneL-field for each RLC PDUs and/or PDU segments except for the last one.

On the receiver side, as shown in FIG. 7 (LI fields are not shown sincethe Example of FIGS. 6-9 relates to segmentation rather thanconcatenation), the MAC layer knows where the actual data starts sinceit knows both the header length, as well as—with the L-field—the MAC PDUlength. The header length is assumed to be known here. For instance, itmay be predefined (for instance specified in a standard) and/orindicated within a field in the header. In the above example, theextension bit is used to indicate whether the header continues orterminates, which makes possible to determine the header size.

The MAC layer performs de-multiplexing of the MAC PDUs without removingthe segmentation fields (SO and LSF) and then the de-multiplexed RLCPDUs/segments are delivered to the RLC layer. When the receiving RLClayer receives the RLC PDU segments, it first reorders and re-assembliesthem if they are received out of sequence (cf. also FIG. 9). One of theadvantages of not doing reordering and reassembling in the MAC layer isthe processing time reduction. If one segment is missed in the receiverside, then the MAC layer could not do reassembly and reordering whichwill add delay in delivery to the upper layer (RLC). In order not todelay re-assembling and re-ordering, the MAC layer passes thesegmentation fields (SO, LSF) to the RLC layer since segmentation andconcatenation are performed by the MAC layer, as described above withreference to FIG. 6. Therefore, the RLC layer reads the segmentationheader field(s) received from the MAC layer and on the basis of thesegmentation (e.g. SO, LSF) and concatenation (e.g. LI) header field(s),the RLC layer performs, where appropriate, the re-ordering andre-assembling. Accordingly, a cross-layer interaction is required inthis example since the receiving RLC layer has to know and use the MAClayer signaling fields.

Any RLC PDUs received out of sequence at the MAC layer are delivered tothe upper layer (RLC). An ARQ operation is performed in the receivingRLC to support an error free transmission (acknowledged mode). In orderto enable the transmitting side to retransmit only the missing RLC PDUs,the receiver side provides an RLC status report to the transmitting sideindicating the missing PDU(s) or PDU segment(s) information for the RLCPDUs.

In response to a status report with one or more PDUs/segments missing,the transmitter of the RLC layer takes the complete RLC PDU of thecorresponding missing packet from the transmission buffer and performs(re)segmentation on the basis of the missing segment(s) which is/areindicated by the RLC status report. If re-segmentation is performedafter the reception of the status report, the RLC changes the RF fieldfrom 0 to 1. Then the (re)segmented PDU(s) is/are delivered to the MAClayer, which reads the RF flag. Since the radio conditions maydeteriorate during the retransmission procedure, the missing segment PDUor PDUs may have to be broken up into smaller segmentations(re-segmented) before retransmission (which is done by MAC layer). Thisis illustrated in FIG. 8, in which the missing 400 byte payload RLC PDUis taken at the RLC layer from the original 1200 byte payload RLC PDU inthe retransmission buffer and further broken (re-segmented) into thesmaller 200 byte payload MAC PDUs.

Re-Segmentation in the MAC Layer

When looking at FIG. 8, it can be seen that the RLC overhead is slightlyincreased, since the RLC transmitter performs the re-segmentation on thebasis of the missing part of the segment, i.e. on the basis of the 400bytes long data which was not received correctly and which is indicatedby the RLC status report and then delivered to the MAC layer.Accordingly, the re-segmentation header (including SO, RF and LSF) isrequired in the RLC, which increases the RLC header overhead.

In order to reduce the overhead, according to an embodiment, there-segmentation is performed in the MAC layer.

In particular, according to this embodiment, a data transmitting node isprovided for transmitting data over a wireless interface in acommunication system to a data receiving node. The data transmittingnode comprises a third layer processing unit for performing an automaticrepeat request, ARQ, retransmission according to a status report fedback from the data receiving node. The data transmitting node furthercomprises a second layer processing unit for receiving, from the thirdlayer processing unit, a third layer data unit, segmenting the thirdlayer data unit according to the status report and based on a resourceallocation and forming a plurality of second layer data units includingthe respective segments of the segmented third layer data unit. Thefirst layer processing unit is also present for receiving from thesecond layer the plurality of the second layer data units and mappingthe plurality of the second layer data units onto the resourcesallocated for data transmission.

Accordingly, the segmentation functionality is entirely transferred tothe second layer, the closest layer to the physical layer. This isillustrated in FIG. 10 in a greater detail based on a selected example.

The RLC layer of the transmitter adds the PDCP PDU (RLC SDU) a headerincluding the polling bit (if this embodiment is applied with AM ratherthan UM) to request a status report and the D/C field indicating whetherthe RLC PDU carries payload (user) or control data. It is noted that thepresent disclosure is not limited to the RLC layer preforming ARQ sincethe RLC layer may also operate in the unacknowledged mode.

The RLC TX layer delivers the status report received from the RLC RX tothe MAC layer. The MAC layer reads the segmentation information such asthe sequence number (SN), SOstart and SOend value form the status reportand performs the segmentation accordingly. Therefore, the RLC TX takesthe complete RLC PDU from the retransmission buffer and sends it to theMAC TX. This is illustrated in FIG. 10 which shows the RLC PDU includingthe data field with PDCP SDU data of 1200 bytes rather than only the 400bytes as shown in FIG. 8.

Afterwards, the MAC TX layer performs the segmentation on the basis ofthe segmentation information, e.g. SOstart, SOend and SN which isindicated by the RLC status report and forwarded down to the MAC layerby the RLC layer as shown in FIG. 10. In accordance therewith, the MACPDU header is generated. The header in FIG. 10 includes the LCID(logical channel identification), the E-bit indicating whether or notfurther header information is present and the segmentation informationincluding here the segment offset (may be in the units of bytes) whichindicates the start of the carried segment within the RLC PDU and thelast segment field (LSF) indicating whether or not the encapsulated RLCPDU segment is the last in the RLC PDU. As can be seen in FIG. 10, theoffsets of 801 and 1001 doe the two segments of 200 and 200 bytesrespectively are signaled.

FIG. 11A shows a status report (STATUS PDU) as defined in the 3GPP TS36.322, v. 13.2.0. STATUS PDU consists of a STATUS PDU payload and a RLCcontrol PDU header. RLC control PDU header consists of a D/C and a CPTfield. The STATUS PDU payload starts from the first bit following theRLC control PDU header, and it consists of one ACK_SN and one E1, zeroor more sets of a NACK_SN, an E1 and an E2, and possibly a set of aSOstart and a SOend for each NACK_SN. When necessary one to sevenpadding bits are included in the end of the STATUS PDU to achieve octetalignment.

FIG. 11B shows an exemplary format of an RLC status report. Thisexemplary status report is similar and includes similar fields as theLTE status report which is exemplified in FIG. 11A. The status report ofFIG. 11B differs from the LTE status report in FIG. 11A in that the PDCPsequence number is conveyed rather than the RLC sequence number.

In particular, the status report includes a DIG field and a CPT (controlPDU type) field which indicates whether or not the PDU is a status PDU,it indicates the status PDU for the status report. PDCP ACK_SN is a 10bits long field which indicates the SN of the next not received RLC DataPDU which is not reported as missing in the status report (STATUS PDU).The prefix “PDCP” here emphasizes that a common SN is used for the RLCand the PDCP layer which is thus also applied to the status report.

Extension bit 1 (E1) indicates whether or not a set of PDCP NACK_SN, E1and E2 follows; if set to 0—a set of NACK_SN, E1 and E2 does not follow;if set to 1—a set of NACK_SN, E1 and E2 follows.

Negative Acknowledgement SN (NACK_SN), in this example PDCP NACK_SNfield, indicates the SN of the RLC PDU (or portions of it) that has beendetected as lost at the receiving side of the AM RLC entity.

Extension bit 2 (E2) indicates whether or not a set of SOstart and SOendfollows; if set to 0—a set of SOstart and SOend does not follow for thisNACK_SN: if set to 1—a set of SOstart and SOend follows for thisNACK_SN.

According to 36.322, sections 6.2.2.18, 6.2.2.19 describe these SOstartan SOend as follows:

SOstart (15 bits): The SOstart field (together with the SOend field)indicates the portion of the RLC PDU with SN=NACK_SN (the NACK_SN forwhich the SOstart is related to) that has been detected as lost at thereceiving side of the AM RLC entity. Specifically, the SOstart fieldindicates the position of the first byte of the portion of the RLC PDUin bytes within the Data field of the RLC PDU.

SOend (15 bits): The SOend field (together with the SOstart field)indicates the portion of the RLC PDU with SN=NACK_SN (the NACK_SN forwhich the SOend is related to) that has been detected as lost at thereceiving side of the AM RLC entity. Specifically, the SOend fieldindicates the position of the last byte of the portion of the AMD PDU inbytes within the Data field of the RLC PDU. The special SOend value“111111111111111” is used to indicate that the missing portion of theAMD PDU includes all bytes to the last byte of the AMD PDU. In otherwords, the SOstart and SOend indicate respectively the start and the endof the negatively acknowledged RLC PDU segments.

Segment Number

The segment offsets (start and end together) which are typically 30 bitslong which increases MAC sub-header overhead, especially for smallersegments.

In order to reduce the overhead, in this embodiment, the segmentidentification is thus a segment number indicating a sequence number ofthe segment of the third layer data unit within the third layer dataunit. This segment number may be used in the data PDUs as illustrated inthe Figures, i.e. instead of the SO field. However, the segment numbermay also be advantageously used in the status report (STATUS PDU) toreplace the SOstart and SOend.

In one example, the MAC sub-header (i.e. portion of the header relatedto segmentation) is reduced by using a 4 bit long segment number insteadof the 30 bit segment offsets (15 bits of SOstart and 15 bits SOend).Thus, the MAC layer performs segmentation on the basis of the 4 bitsindicating the segment number. The 4 bit segment number allowsdistinguishing a maximum of 16 segments. However the number 4 is onlyfor exemplary purposes here. If more or less segments are necessary forthe corresponding user plane layer architecture, this could be doneusing a higher number of bits. The approach of this embodiment is toreduce the overhead by signaling a segment number for each segmentinstead of the start and end of each segment within the RLC PDU. Sincethe number of segments is certainly smaller than the number of bits inthe RLC PDU to which the offsets are related, overhead is generallysaved by addressing the segments rather than the offset.

The employing of the segment number is illustrated in FIG. 12 for thetransmission side. In particular, FIG. 12 shows an IP packet provided tothe PDCP layer, where it is added a D/C field and the PDCP SN andprovided together with this header information to the RLC layer. The RLClayer encapsulates the PDCP PDU by adding thereto an own headerincluding the D/C field and the polling field. Here, RF field is notnecessary as the segmentation is not performed at the RLC layer. Rather,the RLC PDU1 is provided whole to the MAC layer.

As shown in FIG. 12, in the MAC layer, the RLC PDU is divided into twosegments: segment 0 and segment 1 which containing 800 and 400 bytes,respectively. This segmentation may be performed based on the allocationsize. After the segmentation of the RLC PDU, the transmitting MAC entityincludes the relevant MAC headers to form the MAC PDU. In particular,the header includes a Length Indicator (LI) indicating the length of thesegment, the segment number (e.g. the above described 4 bits), the LastSegment Field (LSF) and a field R set to 0 (which indicates that there-segmentation does not follow) for the included RLC PDU. The LI fieldis needed in case of concatenation where one MAC PDU contains 2 or moreRLC PDUs. In case of segmentation, the grant size is known, so thatreceiver knows the size of grant and can perform the reverse operationaccordingly.

The MAC layer then forms, based on the segmentation information the twoMAC PDUs which are referred as MAC PDU1 and MAC PDU2 in FIG. 12. MACPDU1 and MAC PDU2 are sent to the respective transmission time intervalsTTI0 and TTI1 respectively.

TABLE 6 Table 6: MAC Header fields Length The LI field indicates thelength in bytes of the indicator (LI) corresponding Data field elementpresent in the MAC data PDU delivered/received by MAC entity. E.g. inFIG. 12, the LI of the MAC PDU1 indicates 800 and the LI of the MAC PDU2indicates 400. Extension The E field indicates whether this field is theend of bit (E) the header or another extension follows or not E.g. inFIG. 12, the E field is set since further fields are present in both MACPDU1 and MAC PDU2. R The R field indicates whether re-segmentationfollows or not. R value is initially set to 0. E.g, in FIG. 12, the R =0 since the respective MAC PDU1 and MAC PDU2 are not further segmented.Last segment The LSF is set to 1 to indicate that this is the last field(LSF) segment of the RLC PDU. E.g. in FIG. 12, for MAC PDU, 1 the LSF =0 since MAC PDU1 is not the last RLC PDU segment and for MAC PDU2, theLSF = 1 since MAC PDU2 is the last segment of the RLC PDU. LastRe-segment The LRF is set to 1 to indicate that this is the last field(LRF) re-segment of the RLC PDU. E.g. in FIG. 12, this field is notpresent since the R field was not set. Segment number The segment isassigned segment number 0 to 15. E.g. in FIG. 12, for MAC PDU1 which isthe first RLC PDU segment the segment number has a value of 0 (0000 inbinary notation assuming the length of this field being 4 bits) and forMAC PDU2 which is the second and last RLC PDU segment the segment numberhas a value of 1 (0001 in the binary notation)

FIG. 13 illustrates an exemplary receiver side layer processing for thisembodiment in which the segment numbers are employed instead of thesegment offsets.

As shown in FIG. 13, on the receiver side, MAC PDU1 is receivedcorrectly while MAC PDU2 is lost. The MAC layer delivers MAC PDU1together with the segmentation header (including R, segment number andLSF) to the RLC layer, whereas the RLC layer of the receiving side sendsa status report indicating the missing 800 to 1200 bytes (i.e. MAC PDU2)to the transmitting RLC entity. The RLC layer performs then there-assembly and re-ordering of the RLC segments. Here, only the first800 byte segment is correctly received and thus no reordering has to beperformed in this example.

FIG. 14 shows an exemplary transmitter side layer processing uponreceiving the status report from the data receiving side. As shown inFIG. 14, the RLC layer takes the complete RLC PDU from theretransmission buffer (this is illustrated by the PDCP SDU data of 1200bytes included in the RLC PDU rather than only the missing 400 bytes).The MAC layer performs then a re-segmentation on the basis of the RLCstatus report.

After the re-segmentation of RLC PDU, the transmitting MAC entityincludes the relevant MAC headers in the respective re-segmented MACPDUs to indicate their length (LI), a 3 bits re-segment number, lastre-segment field (LRF) and R=1 (which indicates that a re-segmentationfollows) for the respective included RLC PDUs and forms the MAC PDUswhich are referred as MAC PDU1 and MAC PDU2 in FIG. 14.

If required, the MAC layer may perform re-segmentation of the missingpart of segment number e.g. when the missing segment, as reported in RLCStatus report, cannot fit in the available grant for the correspondingLCID (after running LCP). For this purpose, MAC may use e.g. 3 bits (ormore, if required) to identify “re-segments” of the correspondingsegment of an RLC PDU.

In summary, the second layer processing unit includes into the header ofthe second layer data unit the segment identification comprising are-segment number indicating a sequence number of the segment of thethird layer data unit within the segment of the third layer data unit,the re-segment number being signaled using less bits than the segmentnumber. However, it is noted that this is not to limit the presentdisclosure. The size of the segment number and re-segment number mayalso be the same. Another term, which may be employed for “re-segment”is a “sub-segment” since it is a sub-segment of a segment resulting fromprevious segmentation.

In FIG. 14, alternatively, the segment number may be used for thesegments and the segment offset may be used for the sub-segments insteadof the sub-segment number, since it is assumed that retransmissions arenot as frequent and thus higher overhead may be acceptable.

FIG. 15 shows the receiving side layer processing upon receiving theretransmission of the MAC PDU1 and MAC PDU2 shown in FIG. 14.

As shown in FIG. 15, the MAC layer performs de-multiplexing of MAC PDU1and MAC PDU2 and removes part of their header. However; the MAC layerkeeps the relevant segmentation header fields (R field, segment number,LSF, LRF and re-segment number) since the re-ordering and re-assemblingis performed in the RLC layer. The RLC performs then the re-ordering andre-assembling of the MAC segments and sends the result (PDCP PDU) to thePDCP layer.

Reordering and Reassembly at the Second Layer

According to another embodiment of the present disclosure, the receivingside is further modified. In particular, instead of performing there-ordering and the re-assembly in the RLC layer, the MAC layer performsre-ordering and re-assembly. In that case, cross-layer interaction isnot required. In this configuration, the MAC layer is also responsiblefor performing the retransmission processing. If any parts of thesegments are missed, then the receiving entity of MAC layer sends thestatus report to the MAC TX. The MAC status report will slightly differfrom the RLC status report. In particular, the LCID field will beprovided in the status report to differentiate which status reportbelongs to which LCID (logical channel).

In other words, a data receiving node for receiving data over a wirelessinterface in a communication system from a data transmitting node,comprising: a first layer processing unit for de-mapping one or more ofa plurality of second layer data units from the resources allocated fordata transmission and for providing the one or more of the plurality ofthe de-mapped second layer data units to a second layer processing unit;the second layer processing unit for performing de-multiplexing of aplurality of third layer unit segments and segmentation controlinformation from the one or more of the plurality of second layer dataunits, and forwarding the plurality of the demultiplexed third layerunit segments together with the segmentation control information to athird layer processing unit; Moreover, the second layer processing unitis also performing re-ordering of the plurality of the demultiplexedthird layer unit segments and assembly of the demultiplexed third layerunit segments into a third layer data unit. The second layer processingunit may also be configured to check whether or not the data arereceived correctly and send a status report to the peer second layerentity. This embodiment of the receiver is particularly suitable for thereceiver embodiment with the segmentation/concatenation performed in thesecond layer described above.

Multi-Connectivity/Dual Connectivity for More eNBs Same Bearer to MoreLinks.

In case of multi-connectivity, the PDCP layer distributes duplicatepackets into different eNB.

The following Table 7 describes protocol stack of multi-connectivitywith the main functions of each layer.

TABLE 7 Table 7: Functions of protocol layers supportingmulti-connectivity Functions PDCP TX Header compression SN attachingCiphering Packet segmentation on retransmission RLC TX MAC TXConcatenation/multiplexing Segmentation HARQ transmission MAC RX HARQreception De-multiplexing RLC RX PDCP RX Packet deciphering Segmentbased reordering/reassembly/status reporting Complete PDU basedreordering/status reporting Header decompression

FIG. 16 illustrates transmitting side layer processing for a case of anew transmission of an IP packet 1 in accordance with this embodimentsupporting multi-connectivity.

In particular, the first layer is s physical layer, the second layer isa Medium Access Control, MAC, layer and the third layer is a Packet DataControl Protocol, PDCP, layer. However, it is noted that PDCP and RLClayer may also be combine into one layer, or RLC may perform thefunctionality. The third layer processing unit is configured to providethe same third layer data unit to different lower layer stacks fortransmission, over the wireless interface, to different respective basestations, or, in general data receiving nodes. The lower layer stacksare capable of performing segmentation/reassembly individually andindependently from each other. The lower layer stack may includephysical layer and MAC. However, it may also still include RLC layer.

As also noted above, the layer may be also called differently and havedifferent functions than the current LTE layers. In general, themulti-connectivity has a one layer in common which receives a packerfrom higher layers and provides multiple (more than one) copies of thepacket encapsulated as own PDU to the lower layers of respectivemultiple stacks. The multiple stacks handle segmentation and reassemblyas described in any of the above embodiments and separately andindependently from each other, which ensures that they can adapt totheir respective physical channel conditions and status of datareception.

The third layer advantageously controls the retransmission processing.In the above multi-connectivity scenario it is not necessary that eachlower layer stack at the receiver side receives and reassembles thepacket correctly. It is enough when one of them which collects segmentsof the packets from all other stacks is capable of reassemble thepacket. This provides a kind of diversity and increases the throughput.

As shown in FIG. 16, IP packet 1 is attached to the PDCP header on thePDCP layer and the corresponding PDCP PDU is sent to two different basestations, here eNB1 and eNB2. The base stations eNB1 and eNB2 (networknodes) implement respectively protocol layers as described above(RLC/MAC/PHY). The eNB1 passes the PDCP PDU which corresponds to the RLCPDU1 into two segments MAC PDU1 and MAC PDU2 containing 800 byte and 400bytes respectively. The eNB2 may employ a different segmentation sincethe channel quality in different cells may differ. Thus in this example,eNB2 segments the RLC PDU1 into two segments MAC PDU1 and MAC PDU2containing 500 byte and 700 bytes respectively. The RLC layer, ifworking in acknowledged mode, may be further responsible for ARQfunctionality. However, as described above, the PDCP may control the RLCretransmissions. In particular, each RLC layer (of the respective eNB)may pass the status reports to the PDCP of the master eNB, which decideswhether or not a retransmission is necessary and for which segment ofthe packet. The PDCP then instructs the respective RLC layers to performthe retransmissions accordingly.

FIG. 17 illustrates processing at the receiving side. As shown in FIG.17, eNB1 receives MAC PDU1 which contains 0 to 800 bytes whereas the MACPDU2 with 801 to 1200 bytes is lost. On the other hand, eNB2 receivesMAC PDU1 containing 0 to 500 bytes whereas 501 to 1200 bytes is lost dueto missing of MAC PDU2. The PDCP layer performs central re-ordering andre-assembling.

An advantage of not performing the reordering and reassembling in theRLC layer in this embodiment is avoiding unnecessary retransmissionsduring multi-connectivity. If reassembling and reordering were performedin the RLC layer, then the RLC layer of both eNBs will send respectiveindividual RLC status reports to the RLC TX (RLC of eNB1 sends statusreport of 801 to 1200 bytes and RLC of eNB2 sends status report of 501to 1200 bytes, so far actual missing part is 801 to 1200 bytes). In thiscase, RLC TX could retransmit more than the required segments which willbe discarded at RLC RX.

To overcome this problem, the RLC layer in this embodiment works astransparently as possible and the central reordering and reassemblingfunctions are carried out in the PDCP layer. In order to perform thereordering and reassembling, the PDCP layer has to understand thesegment header (SO and LSF) of the MAC layer, since the segmentation isbeing performed in the MAC. The PDCP receives the PDUs from MAC layerand performs central reordering and reassembling, similarly as describedin the above embodiments for the RLC layer. It overlaps common segmentsand sends a status report indicating only the missing part of thesegments, i.e. the part which has not been correctly received by any ofthe eNBs.

When looking at FIG. 17, it can be seen that the MAC PDUs includesegmentation information as described above, i.e. SO and LSF. However,similarly as for the other embodiments, the segmentation information mayinclude segment number and length of the segments instead. Moreover,FIG. 15 shows PDCP SN usage also in the RLC layer to reduce overhead.However, the present disclosure is not limited thereto and in generalseparate sequence numbers may be used for the PDCP and the RLC layers asit is the case in the LTE currently. As mentioned above, cross-layerdesign may improve the efficiency of the transmissions. In particular,the status report is advantageously transmitted and received on thelayer (RLC) below the coordinating layer (third, PDCP) and provided tothe coordinating layer for matching the received segments and decidingwhich segments are to be transmitted, Moreover, the MAC segmentationinformation may be passed up to the coordinating layer in order toenable re-ordering and re-assembly, as well as the coordination of theretransmissions.

However, it is noted that the present disclosure may still work, evenwhen slightly less efficiently, if the PDCP does not perform theretransmission coordination and if the segments are indeed retransmittedredundantly on each link. Advantageously, in FIG. 17, the PDCP RX sendsa status report of missing 801 to 1200 bytes. Advantageously, thisstatus report is send to both (in general multiple) eNBs, so thatdiversity is achieved by retransmission over both links. However, thepresent disclosure is not limited thereto and generally, for the purposeof the retransmission, single connectivity may be re-established.

As shown in FIG. 18, the PDCP TX, upon reception of the status report,takes a complete PDCP PDU (1200 bytes) from the transmission buffer andperforms a re-segmentation (extraction) of the 800 to 1200 bytes whichare indicated by the PDCP status report and then the PDU segment of800-1200 bytes (re-segmented PDU) is delivered to the MAC. The MAC layerof each eNB performs its own segmentation according to the resourceallocation as described in the above embodiments. In this case, as canbe seen in FIG. 18, the fits MAC entity (transmitting to eNB1) segmentsthe 800-1200 bytes to two MAC PDUs, namely in MAC PDU1 with 800 to 900bytes and a second MAC PDU2 with 901 to 1200 bytes. On the other hand,the second MAC entity (transmitting to eNB2) segments the 800-1200 bytesto a first MAC PDU1 with the bytes 801-1000 and a second MAC PDU2 withthe bytes 1001 to 1200.

In general, there are also alternatives: As described above, the PDCPtakes the complete PDU from retransmission buffer and then performsre-segmentation of the missing packet, which is indicated by PDCP statusreport.

However, alternatively, the PDCP status report may be understood by theMAC layer and therefore, the PDCP passes the complete PDU to the MAC,rather than doing the re-segmentation. The MAC will perform segmentationbased on the PDCP status report then.

Still another possibility is that the PDCP will inform the RLC about themissing part(s) of segments. Afterwards, the RLC layer will send thestatus report to the RLC TX.

Correspondingly, FIG. 19 shows receiving side (network side in thisuplink data transmission example) upon reception of the retransmissionsof FIG. 18. In particular, in this example, all segments are receivedcorrectly at the MAC and demultiplexed. The RLC basically passes thereceived segments together with the segmentation information receivedfrom the MAC to the PDCP and the PDCP performs the re-ordering andreassembly of all segments received from all nodes of themulti-connection (here eNB1 and eNB2).

FIG. 20 illustrates the transmitting apparatus 2000 t and the receivingapparatus 2000 r being parts of a communication system 2000 andcommunicating over a channel 2090. In particular, the fourth layerprocessing unit 2040 t, the third layer processing unit 2030 t, thesecond layer processing unit 2020 t and the first layer processing unit2010 t perform the processing of the corresponding layers as describedin the embodiments above. The transmitter 2050 transmits via itsantenna(s) the signal mapped onto the physical resources. The receivingapparatus 2000 r correspondingly comprises the fourth layer processingunit 2040 r, the third layer processing unit 2030 r, the second layerprocessing unit 2020 r and the first layer processing unit 2010 r and areceiver 2060 which receives the transmitted signal over its antenna(s).

FIG. 21 exemplifies one of the embodiments of methods according to thepresent disclosure. In particular, at the left hand side, a methodperformed at the data transmitting side is illustrated while on theright hand side a method performed at the data receiving side isexemplified.

The transmitting method may include steps performed by the third layerincluding receiving 2110 t a third layer SDU, generating 2120 t a PDUbased thereon for instance by appending a header and passing 2130 t thePDU to the second layer. The second layer processing then may includereceiving the third layer PDU as a second layer SDU 2140 t, performingsegmentation or concatenation 2150 t as described above, based on thereceived allocation (and in some embodiments also based on the statusreport) and passing the so formed PDU to the first layer in step 2160 t.The first layer processing then includes receiving 2170 t the SDU fromthe second layer, mapping it to the physical resources 2180 t andtransmitting 2190 t.

At the receiver, as a part of the first layer processing, the reception2190 r is performed, then the data are demapped from the physicalresources 2180 r and passed 2170 r to the second layer. The second layerprocessing includes receiving 2160 r the PDU, demultiplexes it 2150 rand passes 2140 r to the third layer for reordering and reassembly (asdescribed above, in one alternative embodiment, the reordering andreassembly is also performed in the second layer). The third layerprocessing includes receiving the PDU 2130 r, performing the reorderingand reassembly 2120 r and passing the reassembled packet to the upperlayers 2110 r.

Moreover, there are embodiments which implement retransmission mechanismon the third layer, including transmission of a status report at thedata receiving side and receiving 2128 t the status report at the datatransmitting side. If the status report includes negativeacknowledgement for some segments (2125 t, “yes”), the re-segmentation sperformed on the third layer (alternatively, in some embodiments in thesecond layer).

In one general aspect, the techniques disclosed here feature a datatransmitting node that is provided for transmitting data over a wirelessinterface in a communication system to a data receiving node, the datatransmitting node comprising: a third layer processing unit forperforming an automatic repeat request, ARQ, retransmission according toa status report fed back from the data receiving node; a second layerprocessing unit for receiving, from the third layer processing unit, athird layer data unit, segmenting the third layer data unit according tothe status report and based on a resource allocation and forming aplurality of second layer data units including the respective segmentsof the segmented third layer data unit; and a first layer processingunit for receiving from the second layer one or more of the plurality ofthe second layer data units and mapping the one or more of the pluralityof the second layer data units onto the resources allocated for datatransmission.

In one general aspect, the techniques disclosed here feature a datareceiving node that is provided for receiving data over a wirelessinterface in a communication system from a data transmitting node, thedata receiving node comprising: a first layer processing unit forde-mapping one or more of a plurality of second layer data units fromthe resources allocated for data transmission and for providing the oneor more of the plurality of the de-mapped second layer data units to asecond layer processing unit; the second layer processing unit forperforming de-multiplexing of a plurality of third layer unit segmentsand segmentation control information from the one or more of theplurality of second layer data units, and forwarding the plurality ofthe demultiplexed third layer unit segments together with thesegmentation control information to a third layer processing unit; thethird layer processing unit for performing re-ordering of the pluralityof the demultiplexed third layer unit segments and assembly of thedemultiplexed third layer unit segments into a third layer data unit.

Moreover, in one general aspect, the techniques disclosed here feature amethod that is provided for transmitting data over a wireless interfacein a communication system to a data receiving node, the methodcomprising: performing a third layer processing including performing anautomatic repeat request, ARQ, retransmission according to a statusreport fed back from the data receiving node and for re-segmenting ornot data to be retransmitted based on segment length informationincluded in the status report including adding to the data asegmentation control information; performing a second layer processingincluding receiving, from the third layer processing unit, a third layerdata unit, segmenting the third layer data unit based on a resourceallocation and forming a plurality of second layer data units includingthe respective segments of the third layer data unit and thesegmentation control information which is modified if re-segmentation isto be applied; and performing a first layer processing includingreceiving from the second layer one or more of the plurality of thesecond layer data units and mapping the one or more of the plurality ofthe second layer data units onto the resources allocated for datatransmission.

Still further, in one general aspect, the techniques disclosed herefeature a method that is provided for transmitting data over a wirelessinterface in a communication system to a data receiving node, the methodcomprising: a third layer processing including performing an automaticrepeat request, ARQ, retransmission according to a status report fedback from the data receiving node; a second layer processing includingreceiving, from the third layer processing unit, a third layer dataunit, segmenting the third layer data unit according to the statusreport and based on a resource allocation and forming a plurality ofsecond layer data units including the respective segments of thesegmented third layer data unit; and a first layer processing includingreceiving from the second layer one or more of the plurality of thesecond layer data units and mapping the one or more of the plurality ofthe second layer data units onto the resources allocated for datatransmission.

Furthermore, in one general aspect, the techniques disclosed herefeature a method for receiving data over a wireless interface in acommunication system from a data transmitting node, the methodcomprising: a first layer processing including de-mapping one or more ofa plurality of second layer data units from the resources allocated fordata transmission and for providing the one or more of the plurality ofthe de-mapped second layer data units to a second layer processing unit;the second layer processing including performing de-multiplexing of aplurality of third layer unit segments and segmentation controlinformation from the one or more of the plurality of second layer dataunits, and forwarding the plurality of the demultiplexed third layerunit segments together with the segmentation control information to athird layer processing unit; the third layer processing includingperforming re-ordering of the plurality of the demultiplexed third layerunit segments and assembly of the demultiplexed third layer unitsegments into a third layer data unit.

Moreover, a computer readable medium is provided for storing thereininstructions, which when executed on a computer, cause the computer toperform the steps of the above methods.

Hardware and Software Implementation of the Present Disclosure

Other exemplary embodiments relate to the implementation of the abovedescribed various embodiments using hardware and software. In thisconnection a user terminal (mobile terminal) and an eNodeB (basestation) are provided. The user terminal and base station is adapted toperform the methods described herein, including corresponding entitiesto participate appropriately in the methods, such as receiver,transmitter, processors.

It is further recognized that the various embodiments may be implementedor performed using computing devices (processors). A computing device orprocessor may for example be general purpose processors, digital signalprocessors (DSP), application specific integrated circuits (ASIC), fieldprogrammable gate arrays (FPGA) or other programmable logic devices,etc. They may include a data input and output coupled thereto. Thevarious embodiments may also be performed or embodied by a combinationof these devices.

Further, the various embodiments may also be implemented by means ofsoftware modules, which are executed by a processor or directly inhardware. Also a combination of software modules and a hardwareimplementation may be possible. The software modules may be stored onany kind of computer readable storage media, for example RAM, EPROM,EEPROM, flash memory, registers, hard disks, CD-ROM, DVD, etc.

It should be further noted that the individual features of the differentembodiments may individually or in arbitrary combination be subjectmatter to another embodiment.

It would be appreciated by a person skilled in the art that numerousvariations and/or modifications may be made to the present disclosure asshown in the specific embodiments. The present embodiments are,therefore, to be considered in all respects to be illustrative and notrestrictive.

Summarizing, the present disclosure relates to layer processing at areceiver and a transmitter in a communication system. The layerprocessing includes at least processing on a first, a second and a thirdlayer. At the transmitter side, the third layer receives a packet, addsits header and forwards the packet to the second layer. The second layerperforms segmentation and provides segmented data to the first layer,which maps the segmented data onto physical resources. The segmentationis based on the allocated resources. Retransmissions may take place onthe third layer and thus, the third layer may re-segment the packetaccording to the received feedback for particular segments and providethe re-segmented data to the lower layers. Alternatively, the feedbackinformation is provided to the second layer which then performs thesegmentation by taking it into account. Correspondingly, the receiverperforms re-ordering and re-assembly at the third layer for which itreceives also control information from the second layer.

What is claimed is:
 1. A data transmitting node for transmitting dataover a wireless interface in a communication system to a data receivingnode, comprising: a third layer processing circuit which in operation,performs an automatic repeat request, ARQ, retransmission according to astatus report from the data receiving node and re-segments dataretransmitted based on segment length information included in the statusreport including adding to the data segmentation control information; asecond layer processing circuit which, in operation, receives, from thethird layer processing circuit, a third layer data unit, segments thethird layer data unit into a plurality of segments based on a resourceallocation, and forms a plurality of second layer data units includingthe respective segments of the third layer data unit and thesegmentation control information which is modified if re-segmentation isapplied; a first layer processing circuit which, in operation, receivesfrom the second layer processing circuit, one or more of the pluralityof the second layer data units and maps the one or more of the pluralityof the second layer data units onto the resources allocated for datatransmission; and a transmitter which, in operation, transmits the datamapped onto the allocated resources; wherein the third layer processingcircuit, in operation, adds into the third layer data unit a headerincluding one or more of: an indication of whether the included data arecontrol or payload data, an indication of whether a status report isrequested for the transmitted data, and an indication of whether thethird layer data unit includes an entire higher layer data unit or asegment of a higher layer data unit; wherein the second layer processingcircuit, in operation, adds into each second layer data unit of theplurality of second layer data units a header including one or more of:a segment identifier indicating the segment of the third layer data unitcarried by the second layer data unit, and a flag indicating whether thesegment of the third layer data unit carried by the second layer dataunit is a last segment of the third layer data unit, and wherein thesecond layer processing circuit, in operation, adds into at least one ofthe second layer data units a plurality of third layer data units and alength field indicating a length of each the third layer data units. 2.The data transmitting node according to claim 1, wherein: the firstlayer processing circuit is a physical layer processing circuit, thesecond layer processing circuit is a Medium Access Control, MAC, layerprocessing circuit and the third layer processing circuit is a PacketData Control Protocol, PDCP, layer processing circuit, the third layerprocessing circuit, in operation, provides a same third layer data unitto different lower layer stacks for transmission, over the wirelessinterface, to different respective base stations and to controlretransmission processing, the lower layer stacks perform segmentationand reassembly individually and independently from each other.
 3. Thedata transmitting node according to claim 1, wherein: the first layerprocessing circuit is a physical layer processing circuit, the secondlayer processing circuit is a Medium Access Control, MAC, layerprocessing circuit and the third layer processing circuit is a RadioLink Control, RLC, layer processing circuit, the data transmitting nodefurther comprises a fourth layer circuit which, in operation, provides asequence number, the fourth layer processing circuit being a Packet DataControl Protocol, PDCP, layer processing circuit, the third layerprocessing circuit does not provide another sequence number andencapsulates the fourth layer data unit including the sequence numberprovided by the PDCP layer processing circuit.
 4. The data transmittingnode according to claim 3, wherein the status report includes a positiveor a negative acknowledgement for at least one segment of the thirdlayer data unit encapsulated in the fourth layer data unit identified bythe sequence number.
 5. A data transmitting node for transmitting dataover a wireless interface in a communication system to a data receivingnode, comprising: a third layer processing circuit which, in operation,performs an automatic repeat request, ARQ, retransmission according to astatus report fed back from the data receiving node; a second layerprocessing circuit which, in operation, receives, from the third layerprocessing circuit, a third layer data unit, segments the third layerdata unit into a plurality of segments according to the status reportand based on a resource allocation, and forms a plurality of secondlayer data units including the respective segments of the third layerdata unit; wherein the second layer processing circuit adds into aheader of each of the second layer data units a segment identifiercomprising a segment number indicating a sequence number of a segment ofthe third layer data unit within the third layer data unit, and whereinthe second layer processing circuit adds into the header of each of thesecond layer data units the segment identifier comprising a re-segmentnumber indicating a sequence number of the segment of the third layerdata unit within the segment of the third layer data unit, there-segment number being signaled using less bits than the segmentnumber; a first layer processing circuit which, in operation, receivesfrom the second layer processing circuit one or more of the plurality ofthe second layer data units and maps the one or more of the plurality ofthe second layer data units onto the resources allocated for datatransmission; and a transmitter which, in operation, transmits the datamapped onto the allocated resources.
 6. A data receiving node,comprising: a receiver which, in operation, receives data over awireless interface in a communication system from a data transmittingnode; a first layer processing circuit; a second layer processingcircuit; and a third layer processing circuit; wherein the first layerprocessing circuit, in operation, de-maps one or more of a plurality ofsecond layer data units from resources allocated for data transmissionand provides the one or more of the plurality of second layer data unitsto the second layer processing circuit; wherein the second layerprocessing circuit, in operation, de-multiplexes a plurality of thirdlayer unit segments and segmentation control information from the one ormore of the plurality of second layer data units, and forwards theplurality of the third layer unit segments together with thesegmentation control information to the third layer processing circuit;wherein the third layer processing circuit, in operation, re-orders theplurality of the third layer unit segments and assembles the third layerunit segments into a third layer data unit; wherein the third layerprocessing circuit, in operation, generates control data carrying astatus report indicating whether at least one third layer unit segmenthas been received correctly and provides the generated status report tothe second layer processing circuit for transmission over the wirelessinterface to the data transmitting node; and wherein the status reportincludes positive acknowledgements or negative acknowledgements for atleast one third layer data unit, or an identifier of correctly receivedor missing segments of the third layer data unit.
 7. The data receivingnode according to claim 6, wherein the segmentation control informationincludes one or more of: a segment offset indicting an offset in bytesof a third layer unit segment within the third unit data unit; a segmentnumber indicating a sequence number of the segment of the third layerdata unit within the third layer data unit; a length of the segment; andan indicator of whether the third layer segment is a last segment in thethird layer data unit.
 8. A method for transmitting data over a wirelessinterface in a communication system to a data receiving node,comprising: performing an automatic repeat request, ARQ, retransmissionaccording to a status report from the data receiving node andre-segmenting data retransmitted based on segment length informationincluded in the status report including adding to the data segmentationcontrol information; segmenting a third layer data unit based on aresource allocation and forming a plurality of second layer data unitsincluding the respective segments of the third layer data unit and thesegmentation control information which is modified if re-segmentation isapplied; mapping the one or more of the plurality of the second layerdata units onto resources allocated for data transmission; adding intothe third layer data unit a header including one or more of: anindication of whether the included data are control or payload data, anindication of whether a status report is requested for the transmitteddata, and an indication of whether the third layer data unit includes anentire higher layer data unit or a segment of a higher layer data unit;adding into the second layer data unit a header including one or moreof: a segment identifier indicating the segment of the third layer dataunit carried by the second layer data unit, and a flag indicatingwhether the segment of the third layer data unit carried by the secondlayer data unit is a last segment of the third layer data unit, andadding into at least one of the second layer data units a plurality ofthird layer data units and a length field indicating a length of eachthe third layer data units.
 9. A method for transmitting data over awireless interface in a communication system to a data receiving node,comprising: performing an automatic repeat request, ARQ, retransmissionaccording to a status report fed back from the data receiving node;segmenting a third layer data unit according to the status report andbased on a resource allocation and forming a plurality of second layerdata units including the respective segments of the third layer dataunit; adding into a header of each of the second layer data units asegment identifier comprising a segment number indicating a sequencenumber of a segment of the third layer data unit within the third layerdata unit; mapping the one or more of the plurality of the second layerdata units onto the resources allocated for data transmission; andadding into the header of each of the second layer data units thesegment identifier comprising a re-segment number indicating a sequencenumber of the segment of the third layer data unit within the segment ofthe third layer data unit, the re-segment number being signaled usingless bits than the segment number.
 10. A method for receiving data overa wireless interface in a communication system from a data transmittingnode, comprising: de-mapping, by a first layer processing circuit, oneor more of a plurality of second layer data units from resourcesallocated for data transmission and providing the one or more of theplurality of second layer data units to a second layer processingcircuit; de-multiplexing, by the second layer processing circuit, aplurality of third layer unit segments and segmentation controlinformation from the one or more of the plurality of second layer dataunits, and forwarding the plurality of the third layer unit segmentstogether with the segmentation control information to a third layerprocessing circuit; re-ordering, by the third layer processing circuit,the plurality of the third layer unit segments and assembling the thirdlayer unit segments into a third layer data unit; and generating, by thethird layer processing circuit, control data carrying a status reportindicating whether at least one third layer unit segment has beenreceived correctly, and providing the generated status report to thesecond layer processing circuit; wherein the status report includespositive acknowledgements or negative acknowledgements for at least onethird layer data unit, or an identifier of correctly received or missingsegments of the third layer data unit.